Described herein are genes shown to be essential for programmed cell death in C. elegans, their encoded products (RNA and polypeptides), antibodies directed against the encoded polypeptides; probes for identifying structurally related genes and bioassays for identifying functionally related cell death genes from various organisms; methods and agents for altering (increasing or decreasing) the activity of the cell death-genes and, thus, of altering cell death; and uses therefor. Specifically, two genes shown to be essential for almost all of the cell deaths which occur in the development of C. elegans, referred to as ced-3 and ced-4, have been cloned, sequenced and characterized.