Podophyllotoxin (CPH86), at concentrations of 5 ng/ml or more, inhibited [3H]-thymidine uptake of ConA-induced proliferation of human peripheral mononuclear blood cells. Tween80, the detergent included in the anti-inflammatory drug Proresid, containing podophyllum lignan derivatives, also inhibited lymphocyte proliferation in a dose-dependent manner. Combination of the two drugs did not, or did only weakly, potentiate the inhibitory effect of each drug.