CTLA-4 and CD28 are T lymphocyte receptors involved in the regulation of T-cell activation. Allograft rejection is an alloimune response which is strongly dependent on T-cell proliferation. Thus, we examined the relationship between CTLA-4 and CD28 gene polymorphisms and renal transplant outcomes. We genotyped 141 renal recipients and 229 healthy controls using PCR-SSP methods for the (-318) C/T polymorphism in the promoter region of the CTLA-4 gene and IVS3 (+17) T/C on intron 3 of the CD28 gene, and by PCR-RFLP method for exon 1 (+49) A/G and CT60 G/A within the 3'-untranslated region (UTR) of the CTLA-4 gene. Patients were classified into two groups: Group I included 23 HLA-identical haplotype allograft recipients and group II, 118 recipients with one or more mismatches in HLA haplotypes. Thirty-six patients developed at least one acute rejection episode (ARE). No significant differences were observed between the genotypes or the allele distribution between ARE and non-ARE patients. However, in group I, (+49) A and CT60 (G) allele frequencies were lower in patients with ARE than those without ARE (0.100 and 0.400 vs 0.361 and 0.722 respectively). However, the difference was not significant. Our study suggested that these alleles may confer protection against renal allograft loss.