Apoptosis is a distinct morphological and biochemical entity resulting in cell death, which occurs because of a variety of pathological and physiological stimuli. Chemotherapeutic agents, at least in part, result in cell death by inducing apoptosis. Quantitation of this process enables the study of differential cellular responses to chemotherapy and potentially clinical sensitivity. Apoptotic process results in cytoskeletal disruption, cell shrinkage, membrane blebbing, nuclear condensation, and internucleosomal DNA fragmentation. A variety of methods exist to determine apoptosis along this pathway. Diphenylamine assay enables the quantitation of degraded DNA. The protocol is simple and allows manipulation of all types of cell cultures. Resulting colorimetric reaction is easily quantitated, and the assay is highly reproducible.