Sixty-nine asymptomatic HBsAg carriers have been studied for the presence of laboratory stigmata of connective tissue disorders. Anti-nuclear antibodies accompanied by a significant binding of anti-DNA were detected on one carrier only. In contrast, rheumatoid activity was detected in 10 out of 63 carriers, and lymphocytotoxins in 8 out of 33. Carriers had a significantly increased level of circulating immune complexes associated with mild hypocomplementemia. Since none of the carriers had any evidence of liver disease, it is probable that the immunologic abberations were induced by the persistent viral infection rather than liver injury. It seems that some asymptomatic carriers have an occult laboratory-wise, connective tissue disorder which, under yet unknown circumstances, gives rise to an overt immune complex disease.