"In helping to create the book for an American audience, she needed him to explain a lot of the material and he was able to do so in a way that checked out," he said.

Some of the descriptions in the book, minus the numerous details on Mao's very active sex life, have appeared in other memoirs, especially those concerning Mao's imperial way of life, his residence and swimming pool in Zhongnanhai, his chronic insomnia and the very odd hours that he kept, as well as the atmosphere of sycophancy that surrounded him. But nobody before has provided anything like the full, elaborately detailed portrait that Dr. Li presents in his book.

"Here's a picture of the daily life of a man who has absolute power, and the fascinating thing is how absolute power sort of deranges the possessor of it, so that the boundary between fantasy and reality is obliterated because there's nothing to check his will," Professor Nathan said. "He was insulated in his own cocoon while everybody danced to his whims, and that has a lot to do with the tremendous disasters Mao wrought on the country as a whole because he was insulated from reality. His fantasies became reality."

Indeed, in Dr. Li's voluminous description, Mao emerges as a kind of Chinese Caligula, whose bohemian and decadent life contrasted utterly with the images of it so carefully fashioned by Chinese propaganda. In a Land of Denial, Vast Sexual Excess

The most salacious elements of Mao's career, in Dr. Li's portrait, certainly involve Mao's sexual life, which reached openly lascivious proportions in a country where sexual license was rigorously prohibited for almost everybody else.

Along the way, Dr. Li provides some medical details, including the fact that Mao had an undescended testicle and that he suffered from bouts of impotency. Mao was married three times and had several children but, Dr. Li writes, sometime in midlife, and for undetermined reasons, he became infertile.

"So, I've become a eunuch, haven't I," Dr. Li remembers Mao saying after hearing the news.

Mao, Dr. Li says, used women for three purposes, the first and most important having to do with his pleasure. At Zhongnanhai, and wherever Mao traveled, Dr. Li writes, there were dance parties -- this at a time when ballroom dancing in China was deemed bourgeois and actively discouraged. Young women from cultural troupes or from the Communist Party secretariat, women who Dr. Li says were "selected for their looks, their talent and their political reliability," came to the dances and Mao commonly chose one or more of them to be entertained in his room, or in his special train, or in the guesthouses where he stayed when on one of his many "national inspection tours."