It's the weirdest summer-reading hit in memory. When Derek Humphry's Final Exit: The Practicalities of the Self-Deliverance and Assisted Suicide for the Dying (192 pages. Hemlock Society. $16.95) makes its first appearance in The New York Times best-seller list next Sunday, in the category of Advise, How-to and Miscellaneous, it will already be No. 1.

The person least surprised is the 61-year-old Humphry, principal founder of The Hemlock Society, a right-to-die organization. "I knew the time had come for a really up front book" about suicide, he says--"a nuts-and-bolts book on how to end your life." The book's success comes at the heels of a series of well-publicized suicide cases such as those involving Dr. Jack Kevorkian and Dr. Timothy Quill. The rather pro forma protests against the book by various medical ethicists and the National Right to Life Committee leave Humphry unmoved. "People don't give a damn for all the moralizing in the media and the legislatures," he says. "They want to know when they're in a tight spot."

Filled with charts specifying drug overdoses and a variety of suicide techniques (prescription drugs used in combination with a plastic bag over the head is Humphry's preferred method), "Final Exit" makes chilling reading. Humphry covers every aspect of suicide in unsettling detail. He is particularly keen on etiquette, urging anyone compelled to use a hotel room to leave a note "apologizing for the shock and inconvenience"--- along with a big tip.

Humphry doubts most of the book's readers will ever use it. "They want it on their bookshelf so they can say, "Right, if life becomes too painful or too awful, I can pull it down and make my exit'."