A number of factors have been implicated in the pathogenesis of acute poststreptococcal glomerulonephritis (APSGN). The lack of a reliable animal model has made it difficult to further examine the role of these factors in the pathogenetic process. In this report, we present a tissue cage model in mice for the study of APSGN. Morphological and immunohistological changes in the kidney, resembling those of APSGN in man, were induced at high frequency in the experimental model after infection with group A streptococcal nephritis isolates. Nephritis-associated strain induced hypercellularity, occlusion of capillaries, and C3 deposition at high frequencies compared to the changes induced in animals infected with a non-nephritis-associated strain and non-infected controls. In animals infected with a nephritis isolate, hematuria and proteinuria were also detected. If penicillin treatment was initiated on the third day of infection, the development of the nephritis process was prevented. Streptokinase, as well as preabsorbing antigen and streptococcal pyrogenic exotoxin B (SpeB), have been implicated in the pathogenesis of APSGN. These proteins, as well as SpeA and SpeF, were detected in the fluids of the infectious focus, regardless of the origin of the strains and whether or not glomerulonephritis was seen. Antibodies to streptokinase were evoked in the majority of the infected animals. This immune response did not correlate with the nephritic process since hypercellularity was also seen in animals which lacked detectable streptokinase antibodies. The results show that the mouse tissue cage model can be used to study APSGN and to evaluate factors involved in the pathogenesis of the disease.