A study was performed to elucidate the mechanisms of charge-based immune complex nephritis. A chronological observation after induction of nephritis was made by immunoelectron microscopy to clarify whether antigen (Ag) remains in association with antibody (Ab) and C3 during the translocation through the glomerular basement membrane (GBM). Fifteen minutes after intrarenal perfusion with cationized ferritin (pI> 10.0) as Ag, followed by injection of rabbit anti-ferritin Ab, deposition of subendothelial Ag-Ab-C3 complexes was observed. Between 2 hours and 1 day, a large number of Ag in close association with Ab was noted in the lamina densa, but only a small amount of C3 was detectable. During this time Ag and Ab in the subendothelial region gradually decreased. However, C3 reappeared in the subepithelial region together with the Ag-Ab complex after 1 day, and the subendothelial C3 significantly decreased. At 2 hours and day 1, the distributions of Ag and Ab in the GBM were similar in immersion-fixed kidneys regardless of the preperfusion with phosphate-buffered saline. On the other hand, the passage of Ag across the lamina densa was delayed in the experimental rats as compared with the controls. Significant albuminuria also appeared on day 1. Despite the general concept that Ab binding to cationized Ag results in low avidity immune complex, cationized Ag translocated across the GBM in close association with Ab. The complement was activated biphasically in the subendothelial and in the subepithelial space. The subendothelial complement activation may have contributed to the translocation of immune complex.