It is now well established that the activity of certain liver enzymes displays sex differences and that administration of human growth hormone to male rats alters the liver metabolism in a "female" direction. In this work we studied steroid sulfatase activity and binding of estradiol-17 beta in livers from intact rats and found a sex difference, with considerably higher enzyme activity in male as compared to female liver tissue. Continuous infusion of native and recombinant human growth hormone and estradiol-17 beta to male rats reduced sulfatase activity to "female" levels. A specific binding of estradiol-17 beta with receptor properties was found in the rat livers, but the concentration of binding sites did not change after administration of growth hormone or estradiol in this group of intact animals. Our data confirm previous reports that continuous administration of human growth hormone "feminize" liver metabolism, and since estradiol was found to have an identical effect on sulfatase activity it is suggested that the effect of estradiol-17 beta in this respect may be indirect, mediated via an altered secretory pattern of rat growth hormone.