The plant pathogenic fungus Cochliobolus heterostrophus produces melanin, a black pigment, via 1, 8-dihydroxynaphthalene. The deficiency of C. heterostrophus Brn1^- mutant was complemented with the cosmid clone pCOS/ML6, screened by heterologous hybridization with the genes involved in the melanin biosynthesis of Alternaria alternata. We determined the DNA sequence of the Brn1 gene and its flanking regions. The Brn1 gene contains one open reading frame consisting of three exons separated by two introns. A comparison of the nucleotide and predicted amino acid sequence of the Brn1 gene with those of other fungal reductase genes involved in melanin biosynthesis indicates significant similarity as well as the pathway of melanin biosynthesis.