Pretreatment of rats with desoxypodophyllotoxin for 4 d (day-3 to day 0) has been found to inhibit the increase of serum transaminase activities at 24 h after D-galactosamine injection (day 0) in a dose-dependent manner and to prevent histological deterioration of the liver. In the case of pretreatment with desoxypodophyllotoxin, serum transaminase activities were lower than those of the control group until 24 h after D-galactosamine injection, but rather higher than the control levels afterwards. Successive treatment with desoxypodophyllotoxin for 6 d (day-3 to day 2) markedly inhibited the increase of serum enzyme activities induced by D-galactosamine up to the end of the experiment (day 4). Concerning the mechanism of the liver-protective action of desoxypodophyl-lotoxin, it is suggested that the stabilizing effect of desoxypodophyllotoxin on the plasma membrane may play an important role in protecting the liver from lesions caused by D-galactosamine.