Conditions for polymerase chain-reaction amplification of ten exon regions (Exons 3, 7, 11 through 13, and 15 through 19) of the collagen COL4A5 gene and four exon regions (Exons 2, and 12 through 14) of the COL4A6 gene were sequenced and established in this study. These Type IV collagen genes contain 51 and 48 exons, respectively. The sequences of these exons were determined in the two genes in 250 male patients with hematuria and suspected Alport syndrome. Seventeen mutations were found in nine of the ten exons studied in the COL4A5 gene in 17 patients, whereas no mutations were identified in COL4A6. One mutation was identical in two patients known to be unrelated. The results indicate that mutations in COL4A5 that leading to renal failure are more frequent than those involved in classic Alport syndrome, and also that mutations in COL4A6 are not likely to cause this disease. Furthermore, mutations in COL4A5 are distributed quite randomly and no "hot spots" were found.