Effects of D-galactosamine (GalN) was studied in primary cultures of adult rat hepatocytes. Hepatocytes were isolated by a in situ collagenase perfusion technique and maintained as monolayers in serum free media for 48 hr. To defect the cytotoxicity, effects of GalN on hormonal induction of α-amino isobutyric acid (AIB) transport system and tyrosine aminotransferase (TAT) activity were studied. Effects on uptake of cardiac glycoside, ouabain was also examined. Treatment of GalN inhibited hormonal induction of AIB uptake markedly. At 0.1 mM of GalN, AIB uptake was inhibited significantly when treated for 12 hr. At higher doses (0.25, 0.5 and 1.0 mM) significant inhibition was noticed after 1 hr exposure. Generally the magnitude of the inhibition was dose and treatment time related. Treatment of GalN to the culture also inhibited hormonal induction of TAT activity. The effects was quite similar pattern as in AIB uptake. Meanwhile, uptake of ouabain was not effected by GalN; up to 1 mM of GalN, uptake of ouabain was similar to that of controls. The viability of the hepatocyte was decreased only slightly by the treatment of GalN; more than 87% of the hepatocytes excluded trypan blue when treated 1 mM GalN for 6 hr. GalN-induced depression of AIB uptake and TAT activity was recovered by the addition of uridine to the culture, simultaneously with GalN or after treatment of GalN.