The pathogenetic roles of platelets were studied in unilateral progressive Masugi nephritis in the rabbit. On fourteenth day after the injection of anti-kidney serum, peripheral platelet counts, platelet aggregation and platelet aggregation rate were not changed statistically compared with those before the initial injection. The presence of platelet antigen within the glomeruli of the unclamped nephritic kidney suggests the participation in the pathogenesis of glomerular lesion. No significant difference was observed in the intrarenal uptake of 111Indium-labeled platelets between clamped and unclamped kidneys. This is probably due to the possibility of the participation of the very small amount of platelets or the possible decreased renal blood flow in the nephritic side in this model, or the active uptake of platelet not being found in this progressed stage of this model
