Renal mesangial cell (MC) cultures are easily established and widely used. MC produce some complement (C) regulatory proteins. We studied whether MC synthesize C components (C3, C5, C8). MC cultures were established from normal portions of cortices of nephrectomies for renal cancer. After growing to near-confluence in RPMI/17% FBS and resting for 24 h in RPMI/0.5% FBS, MC were stimulated up to 72 h with IL-1 beta or IL-6 (10, 100, 1000 U/ml). Neither C5 nor C8 were detected by ELISA. While C3 was present in supernatant under basal conditions (15.5-107.6 ng/10(6) cells/24h) in different MC lines. IL-1 beta up-regulated the synthesis by 2.4-4.5 folds, whereas IL-6 did not show any effect. C3 synthetic rate was 1.76 ng/h/10(6) cells under IL-1 stimulation versus basal rate of 0.37 ng/h/10(6) cells. MC production of C3, especially induced by IL-1 may have pathogenetic relevance in glomerulonephritis.