Many of today's medical illnesses can be attributed directly or indirectly to problems with apoptosis--a programmed cell-suicide mechanism. Disorders in which defective regulation of apoptosis contributes to disease pathogenesis or progression can involve either cell accumulation, in which cell eradication or cell turnover is impaired, or cell loss, in which the cell-suicide programme is inappropriately triggered. Identification of the genes and gene products that are responsible for apoptosis, together with emerging information about the mechanisms of action and structures of apoptotic regulatory and effector proteins, has laid a foundation for the discovery of drugs, some of which are now undergoing evaluation in human clinical trials.