The structures of the gene for calpain (CANP-3) and of the DMD gene were analyzed in patients with primary myopathies [limb-girdle muscular distrophy (LGMD) and Duchenne-Becker myodystrophy (DBM)] from various regions of Russia. Via amplification of DNA isolated from the peripheral blood lymphocytes of 74 patients, extended deletions were found in 18 out of 55 patients with DBM. In none of the 19 patients with LGMD, were extended deletions in the CANP-3 gene found. In most patients with LGMD, the amplification of the promoter region and exons 1, 2, 3, 4, 5, and 6 of the CANP-3 gene yielded a single product of corresponding length, but in six patients (three sib pairs), amplification of exon 4 of the CANP-3 gene yielded two products of different size. The following single-strand conformation polymorphism (SSCP) analysis revealed a pronounced polymorphism of exon 4 of the CANP-3 gene in 14 out of 19 patients with LGMD. This structure of exon 4 of the CANP-3 gene was found neither in 16 patients with DBM who had deletions in the DMD gene nor in 16 patients with DBM who had no deletions in the DMD gene.