Experimental and clinical evidence support the role of transforming growth factor beta-1 (TGF-beta(1)), a cytokine with complex immune and nonimmune effects, on the development of chronic renal allograft nephropathy (CAN). We investigated the effects of different immunosuppressive regimens on circulating TGF-beta(1) plasma levels in stable kidney transplant (KTx) recipients. Two hundred ninety-nine TGF-beta(1) plasma levels were measured in 125 kidney transplant (KTX) recipients exhibiting stable renal function, immunosuppressed with cyclosporine (CsA), tacrolimus (TAC), or sirolimus (SIR), and in 18 normal healthy volunteers (C). Activated immunoreactive TGF-beta(1) was detected in platelet-depleted plasma by an enzyme-linked immunoadsorbent assay. Multivariate analyses correlated immunosuppressive regimens with TGF-beta(1) levels. KTX recipients displayed significantly higher TGF-beta(1) levels compared to C (P =.0005). Patients receiving CsA had significantly higher TGF-beta(1) plasma levels compared to those receiving TAC or SIR (P =.0384). Multivariate analyses showed no correlation between TGF-beta(1) levels and immunosuppressive drug trough blood levels or doses, but only correlations with the main immunosuppressive drug. These data show that: (1) TGF-beta(1) production is activated in kidney transplant recipients; (2) CsA patients display significantly higher plasma TGF-beta(1) levels. Follow-up studies seek to assess the possible relationship with clinical events.