There is controversy over whether mesangial cells synthesize and release IL-1 and TNF, and many of the positive experiments were performed before specific reagents and molecular probes were available. Consequently we have stimulated human mesangial cells using protocols known to stimulate the synthesis of other cytokines. No mRNA for IL-1 beta or TNF could be detected in quiescent or proliferating mesangial cells irrespective of whether they had been exposed to cytokines or not. In contrast mRNA for IL-1 alpha was detected in cells stimulated with IL-1 beta 10 ng/ml or with TNF 500 ng/ml; IL-1 alpha was also detected in cell lysates from stimulated mesangial cells. We could not detect mRNA for IL-1 receptor antagonist in any of the cell preparations. These results suggest that mesangial cells are unlikely to be a major source of IL-1 beta or TNF.