Rats receiving a single dose of adriamycin (7.5 mg/kg) develop heavy proteinuria and histologic lesions similar to those found in minimal change nephrotic syndrome in humans. We found that whole isolated glomeruli from rats injected with adriamycin secreted an IL-1-like cytokine which closely resembled macrophage IL-1. Maximal IL-1-like activity was detected on day 14 of the experiment when rats were heavily proteinuric. Administration of anti-IL-1 antiserum to rats with adriamycin-induced nephrosis provoked a transient but marked reduction in the urinary protein excretion. Our results indicate that IL-1-could be an important mediator implicated in the development of proteinuria in this experimental nephropathy.