A series of 150 patients with serum hepatitis were examined for the incidence of the Australia antigen (HBsAg) and associations with ABO blood groups, haptoglobin types and occurrence of intestinal serum alkaline phosphatase. Among the patients studied 11.3% were positive for HBsAg. When compared to controls patients with blood group 0 showed a significantly increased risk for serum hepatitis (p < 0.05), while those with group B showed a decreased risk (p < 0.01). The presence of the intestinal fraction of alkaline phosphatase showed a negative association with serum hepatitis (p < 0.01) and there was no significant association between alkaline phosphatase types and ABO groups among the patients. The frequency of the Hp1 gene was significantly increased (p < 0.01) among the patients as compared to controls.