We have previously shown that lymphocytes from idiopathic minimal-lesion nephrotic patients produce a lymphokine (supernatant factor) that increases the 35sulfate uptake in the glomerular basement membrane (GBM). The purpose of this report was to further characterize the supernatant factor by studying the effects of interleukins (IL) 2-4, 6, and 8, granulocyte-macrophage colony stimulating factor, and tumor necrosis factor on the 35sulfate incorporation by rat glomeruli in vitro. A significant increase in GBM 35sulfate uptake was only seen when the glomeruli were cultured with the addition of IL-8 as compared with control cultures 10.8 +/- (SEM) 1.7 and 7.9 +/- 1.4 cpm/micrograms GBM protein, respectively (p < 0.005). IL-8 reproduces the effect of the reported supernatant factor on the GBM 35sulfate uptake. Because IL-8 was detected in the supernatant of peripheral mononuclear cell cultures from idiopathic minimal-lesion nephrotic syndrome patients in relapse and because the increased GBM 35sulfate incorporation induced by the supernatant factor has been abolished by the addition to the culture media of anti-IL-8 neutralizing antibodies, we postulate that IL-8 is the previously described supernatant factor.