Disclosed are human interleukin-1 .beta. converting enzyme like apoptosis proteases-3 and 4 and DNA (RNA) encoding such polypeptides. Also provided is a procedure for producing such polypeptides by recombinant techniques and antibodies and antagonists against such polypeptides. Also provided are methods of using the polypeptides, for example, as an antitumor agent, and antiviral agent, and antibodies and antagonists against such polypeptides for example, for treating Alzheimer's disease, Parkinson's disease, rheumatoid arthritis and head injury. Diagnostic assays for identifying mutations in nucleic acid sequence encoding a polypeptide of the present invention and for detecting altered levels of the polypeptide of the present invention for detecting diseases are also disclosed.