Increased IgA synthesis probably plays a role in the pathogenesis of IgA nephropathy (IgAN). We investigated whether an increased sensitivity to the effect of various growth factor combinations leads to increased immunoglobulin synthesis by peripheral blood mononuclear cells (PBMC) from IgAN patients, in comparison to healthy controls. Although none of the growth factors studied (pokeweed mitogen [PWM], interleukin [IL]-2, IL-6, transforming growth factor-β [TGF-β], and combinations) led to greater IgA synthesis in IgAN patients than in controls, the IgA subclass ratio was shifted in favor of IgA1. In controls, but not in IgAN patients, IL-2 enhanced the production of IgA and IgA1 compared with media alone. This possibly reflects previous in vivo activation by IL-2 in IgAN patients. The suppressive effect of TGF-β on immunoglobulin synthesis was modestly greater in IgAN patients than in controls. Increased production of IL-2 and perhaps other cytokines by T cells in vivo may be responsible for the elevated IgA immune response in these patients. © 1992, National Kidney Foundation, Inc.. All rights reserved.