The exposure of human lymphoid leukemia Molt 4B cells to sesamin and episesamin which were isolated from unroasted sesame seed oil and identified by MS, and 1H and 13C-NMR, led to both growth inhibition and the induction of programmed cell death (apoptosis). Morphological change showing apoptotic bodies was observed in the Molt 4B cells treated with sesamin and episesamin. The fragmentations by sesamin and episesamin of DNA to oligonucleosomal-sized fragments that are characteristics of apoptosis were observed to be concentration-dependent, respectively. Moreover, the amount of the DNA fragments in the sesamin-treated cells was increased from 2 days, while that in the episesamin-treated cells was elevated at 3 days after addition of the compounds. These findings suggest that growth inhibitions by sesamin and episesamin of Molt 4B cells result from the induction of apoptosis in the cells.