Decrease in mean platelet survival time in acute poststreptococcal glomerulonephritis (APSGN). In an attempt to study further the possible participation of platelets in the pathogenesis of acute poststreptococcal glomerulonephritis (APSGN), we studied the platelet survival time, as an index of platelet activation, in 22 patients with APSGN. Mean platelet survival time was computed from the disappearance of radioactivity from blood, sampled serially after injection of autologous 51Cr-labelled platelets. C1q solid phase ELISA and conglutinin (K) solid phase ELISA were used to measure the serum levels of immune complexes. The platelet survival time in APSGN patients was 113 +/- 10 h vs 197 +/- 10 h in the control group (p less than 0.001); 68% of the patients had a shortened platelet survival, lower than 95% confidence limit. There was a significant increase in the platelet survival in the six patients that were studied after recovery from acute nephritic syndrome. There was no significant association between the mean platelet times survival and CICs (circulating immune complexes). Similarly, no significant correlation was found between the mean platelet lifespan and the severity of the glomerular disease, as assessed by the serum creatinine level and the proteinuria. These results support evidence of platelet activation and consumption in APSGN and we suggest that this activation occurs in the glomeruli capillary wall, due to platelet-vascular wall interaction. 