Four cyclopentenone prostaglandins (CPPGs) and PGE(2) caused significant dose-dependent inhibition in growth of human oral squamous carcinoma cells (SCC-15). The rank order of their potency was PGJ(2)>PGA(1)>16, 16-dimethyl PGA(1)>PGA(2)>PGE(2). In a follow-up experiment it was found that the mean per cent inhibition in cell growth by PGJ(2) and Delta(12)-PGJ(2) at 10(-5) M was 61.22 and 63.81, while that of 5-fluorouracil and methotrexate was 36.67 and 38.86, respectively. Delta(12)-PGJ(2) and PGJ(2) induced significant dose-dependent inhibition in nuclear DNA synthesis (i.e. cell proliferation). Combining vitamin E succinate with lower concentrations of CPPGs enhanced significantly their inhibitory effect on nuclear DNA synthesis of cancer cells.