Three different types of immunochemical response were noted in association with recurrent attacks of jaundice in 27 addicts who used amphetamine iv. Type I was characterized by high levels of IgM in serum but no demonstrable hepatitis B antigen (HB Ag) in serum, while another type (II) was associated with this antigen in serum. Both types were associated with the classical histopathologic picture of viral hepatitis. According to results of previous studies on immunoglobulins in viral hepatitis, type I is assumed to represent hepatitis A, while the presence of HB Ag in serum (type II) is considered indicative of hepatitis B. The third type of immunochemical response (III) was characterized by almost normal levels of IgM and no demonstrable HB Ag in serum. This type of reaction had a different pattern in the results of certain biochemical tests for liver function and was also associated with a different histopathologic picture, including Kupffer-cell reaction and lobular infiltration of groups of mononuclear inflammatory cells, but no obvious damage to the parenchymal cells.