We established an experimental model of immune complex glomerulonephritis (ICGN) in rats by daily i.v. administration of 2.0 mg of bovine serum albumin (BSA) for 4 weeks (Yamamoto et al., 1978). In the present study, antigen distribution among various organs was evaluated in the whole course of the experimental rat model using the paired radiolabel technique and the direct immunofluorescent method. In the late stage of chronic serum sickness (CSS), antigen distribution to the liver decreased and that to the glomeruli increased remarkedly whereas hepatic distribution of the antigen was the highest among the organs in the early stage of CSS. BSA distribution in the glomeruli correlated positively with the distribution in blood and there was an inverse relationship between glomerular distribution of BSA and hepatic distribution throughout the course of CSS. These observations may show direct evidence that events in the liver influence the development of ICGN.