OBJECTIVE: We studied the significance of BsmI restriction enzyme polymorphism of the vitamin D receptor (VDR) gene and the XbaI and PvuII polymorphisms of the estrogen receptor (ER) gene in patients with type 2 diabetes (n=49), android type obesity with normal carbohydrate metabolism (n=29) and healthy controls (n=138). METHODS: The distribution of genotypes in the study groups, as well as their relationship to fasting and 1 h postprandial serum C-peptide levels were analyzed. RESULTS: Postprandial serum C-peptide levels of BB genotypes were significantly higher in the diabetes and obese groups (6.18+/-5.09 ng/ml) compared with other genotypes (2.71+/-2.45 vs. 1.72+/-1.97 ng/ml, respectively, P=0.05). Among patients with type 2 diabetes and obese subjects, the XX allelic variant of the ER gene was more frequent (P=0.00015). Postprandial C-peptide levels of subjects exhibiting XX genotype were significantly lower compared with those with Xx genotype (1.67+/-2.16 vs. 3.8+/-3.72 ng/ml, P=0.021). The BBXx allelic combination of the VDR/ER receptor genes was less frequent in diabetic patients than in healthy subjects or in obese patients. The BBXx genotype was associated with significantly elevated postprandial C-peptide levels in all subjects compared with other combinations (9.65+/-3.14 vs. 1.35+/-2.82 ng/ml, P=0.003). No difference was found in the distribution of the PvuII polymorphism of the ER gene or in the association with the C-peptide levels among study groups. CONCLUSION: Polymorphisms of the VDR/ER receptor genes might play a role in the pathogenesis of type 2 diabetes by influencing the secretory capacity of beta-cells.