In Stephen Sondheim’s 1970 musical “Company,” Elaine Stritch raspily sang a toast to the trendy “ladies who lunch,” who fill their days with a “matinee, a Pinter play, perhaps a piece of Mahler’s.” Since then, the Austrian composer and conductor Gustav Mahler (1860–1911) has grown even more fashionable, for his artistically elaborate works which capture the emotional highs and lows of human life. Mahler depicted his worldview in majestic sound, inspired by what he called Naturlaut, or “nature’s voice.” Once despised for his mixing of high and low musical sources, his Jewish origins, and his frequent angst, Mahler today is honored with 203 recordings of his First Symphony, 177 of his Fifth, and 136 of his Second. An abundance of new books also purport to explain how Mahler’s music, which to the casual listener can sound depressing, turns out to be so inspiring.

A reliable, patient guide is needed through the sheer mass of material, which makes the fourth and final volume of the biography by Henry-Louis de La Grange, “Gustav Mahler: A New Life Cut Short, 1907–1911” (Oxford University Press, 1,776 pages, $140), especially welcome. Born in 1924, Mr. de La Grange is an independent scholar and researcher who has written about Mahler in serviceable, although unthrilling, French and English prose for more than four decades. (A further revised version of the 1973 first volume of his Mahler biography is scheduled to appear from Oxford Press by 2011.) “Gustav Mahler: A New Life Cut Short” collects the knowable facts (and many opinions) about Mahler’s life and work, debunking common misconceptions.

One such relates to the composer’s health. In 1907, Mahler was diagnosed by Viennese doctors with a heart condition that was not “inherently fatal.” He subsequently recovered, Mr. de La Grange establishes, and was energetically productive until shortly before his death in 1911 from endocarditis, a bacterial inflammation of the heart unrelated to previous health problems. Most observers have hitherto seen Mahler’s last years (and the works he produced during them, like the Ninth Symphony and “The Song of the Earth”) as inescapably death-laden. Leonard Bernstein, for one, saw Mahler’s Ninth as music by a composer “close to prostration” who knows he is about to “lose it all.” This “sadly pessimistic” view is scorned by Mr. de La Grange, who cites letters, documents, and Mahler’s own statements during this time affirming his “undying faith in man, in art, in music, and in transcendental values.” Bernstein also claimed that the rhythms in Mahler’s Ninth mimic Mahler’s heart arrhythmia, but Mr. de La Grange, who himself suffers from a similar arrhythmia, slates that theory as “downright embarrassing,” as it turns Mahler’s transcendent creation into the mere voicings of a “hypochondriac.”

Previous writers have also claimed that Mahler’s 1908 trip to New York as conductor of the Metropolitan Opera, and afterward the New York Philharmonic, resulted in failure, which hastened his death. Yet as Mr. de La Grange cites from abundant contemporary press sources, Mahler was widely praised as a conductor of the Met’s 1908 “Tristan und Isolde,” although one critic noted about New York audience etiquette, “It is unfortunate that so many found it necessary to enter during the Prelude and leave before the Liebestod.”

Other documents newly uncovered by Mr. de La Grange show Mahler’s unfaithful wife, Alma, to be an even less credible witness than previously believed. Alma’s 1910 love affair with the young architect Walter Gropius was especially duplicitous. Gropius mailed a love letter to Alma in an envelope addressed to her husband, he claimed “by mistake.” Mahler was deeply upset when he read it, and consulted with Sigmund Freud, who punningly pointed out that since Alma’s father was a painter, or “Maler” in German, she naturally married a man named Mahler. (Mahler would also be prey to puns by disapproving Frenchmen such as the composer Claude Debussy, who called him “Malheur,” misfortune in French.)

Further new material here includes a special appendix devoted to a recipe for Mahler’s favorite dessert, apricot dumplings, although the composer’s recurring bouts of hemorrhoids make imitating his diet seem a risky venture. Another appendix, “Mahler Mythomania,” is in the Gallic tradition of the bêtisier, or collection of foolishness, like those compiled by Flaubert and Étiemble. High on the list for ridicule once again is Bernstein, who in his documentary about Mahler, “The Little Drummer Boy,” newly available on DVD from Deutsche Grammophon, claims that Mahler was overcome by guilt after his 1897 conversion to Catholicism from Judaism. Mahler himself downplayed his conversion as something that he “wasn’t all that opposed to … personally.” Other unreliable interpretations of Mahler which Mr. de La Grange poohpoohs include Luchino Visconti’s famous film “Death in Venice,” which identifies Aschenbach, the gay protagonist, with Mahler, supposedly composing his Third Symphony while ogling a boy on the beach. This, according to Mr. de La Grange, shows “misunderstanding not only of the nature of Mahler’s sexual desires, but also of the act of musical creation.” Ken Russell’s 1974 biographical film “Mahler” is likewise dismissed as “endless caricature” in the “schematized world of the cartoon film.”

Countering this kind of derision is hearty approval for a few recent books, such as the psychiatrist Stuart Feder’s “Gustav Mahler: A Life in Crisis” (2004). Yet another helpful and informative appendix, “A Performance History of Mahler’s Works,” details recordings and performances by such pioneering conductors as Bruno Walter, Leopold Stokowski, Artur Rodzinsky, and Dimitri Mitropoulos. Indeed, Mr. de La Grange’s rich and multifarious documentation suggests that Mahler fans should imitate his all-inclusive approach to a composer who said that the symphonic form “must embrace everything.” Must-hear Mahler recordings include those conducted by Rafael Kubelik on Deutsche Grammophon and Audite; Karel An? on Supraphon; Rudolf Barshai on Brilliant; Stokowski on Music & Arts and BBC Legends; Carl Schuricht on Archiphon; Bruno Walter and Otto Klemperer on EMI; Willem Mengelberg on Pristine Audio, and Hans Rosbaud on Wergo. The number of great Mahler recordings now available, like Mr. de La Grange’s heavyweight research, is happy proof of a flourishing posterity for a composer rarely seen as cheery about the future.

Only the subtitle of Mr. de La Grange’s book, “A New Life Cut Short,” may require amendment. Life expectancy in Austria circa 1911 was only around 50, and Mahler did reach that age; moreover, his disciples Schoenberg and Webern agreed that at his death, Mahler’s “work was fully completed.” The magisterial arc of Mr. de La Grange’s narrative leaves the reader with the same overwhelming impression, that in Mahler’s grandiose life and work, nothing whatsoever was cut short.

Mr. Ivry last wrote for these pages on J.S. Bach.