Renal dysfunction is a severe late complication of heart transplantation (HTx). Transforming growth factor beta I (TGF beta I) is a potent multifunctional cytokine with profibrogeneic effect. TGF beta I gene polymorphism correlates with cytokine production. In the present study, we looked for a predictor of renal insufficiency after HTx. In 175 HTx pts and 268 controls, polymorphism in the signal peptide of the TGF beta gene, substitution of leucine-proline at codon 10 and arginine-proline at codon 25, was evaluated by PCR. Renal function was followed after HTx and was compared with the TGF beta I genotypes. There were no differences in the frequencies of alleles and genotypes of TGF beta I gene in the healthy population and HTx recipients; TGF beta I genotype distribution in recipients with ischemic heart disease and dilated cardiomyopathy was almost identical. Renal function was decreasing in most HTx recipients with time. Progression of renal insufficiency (RI) was worse in patients with Leu at codon 10 (LeuLeu vs. LeuPro p < 0.01, LeuLeu vs. ProPro; p < 0.01). RI progression was also more pronounced in individuals homozygous at codon 25 (ArgArg vs. ArgPro; p < 0.01). In individuals heterozygous at codon 10 (LeuPro), the genotype at codon 25 determined the progression of RI (LeuPro/ArgArg vs. LeuPro/ArgPro; p < 0.05). In our study, we have demonstrated the prognostic significance of TGF beta I gene polymorphism for renal insufficiency in heart transplant recipients.