The frequency and spectrum of mutations and the IVS8- T polymorphism of the CFTR gene have been studied in a sample of 963 in Russian infertile men. Mutations have been found in 48 out of 1926 analyzed chromosomes (2.5%) in the heterozygous state (n = 46) and in the compound heterozygote L138ins/N1303K (n = 1/n = 1). A CFTR gene mutation was combined with the 5T allele (mutCFTR/5T) in 11 patients. The following mutations have been found: F508del (n = 18), CFTRdele2,3 (21kb) (n = 9), W1282X (n = 7), 2143delT (n = 4), 3849+10kbC>T (n = 2), L138ins (n = 2), 1677delTA (n = 1), 2184insA (n = 1), 3821delT (n = 1), G542X (n = 1), N1303K (n = 1), and R334W (n = 1). The F508del mutation is the most frequent; it has been detected in 37.5% of the affected chromosomes. The total proportion of four mutations (F508del, CFTRdele2,3 (21kb), W1282X, and 2143delT) is about 79% of all mutations found. The 5T allele has been found in 10.9% infertile men and 4.8% of control men. Significant differences in the frequency of the IVS8-5T variant of the CFTR gene have been found between these groups (p = 0.005), as well as between infertile patients without mutations and control men (p = 0.019). In total, the mutations and/or 5T allele have been found in 14.6% of the patients examined. These data indicate increased frequencies of the mutations of the CFTR gene and its allele variant IVS8-5T in Russian infertile men.