During the biosynthesis of fungal melanin, tetrahydroxynaphthalene reductase catalyzes the NADPH-dependent reduction of 1,3,6,8-tetrahydroxynaphthalene (T4HN) into (+)-scytalone and 1,3,8-trihydroxynaphthalene into (-)-vermelone. The enzyme from Magnaporthe grisea, the fungus responsible for rice blast disease, has been purified to homogeneity. It is a tetramer of four identical 30-kDa subunits. A full-length cDNA clone of about 1 kb encoding T4HN reductase has been isolated from a cDNA library constructed in the lambda ZAP II vector and characterized. The clone contains a 846-bp open reading frame. Translation of the DNA sequence gave a 282-residue amino acid sequence with a calculated molecular mass of 29.9 kDa. Sequences corresponding to the amino-terminal part and three internal proteolytic peptides were present in the translated sequence. T4HN reductase exhibits characteristics of the short-chain alcohol dehydrogenase family. The reductase shares 56% identity with a putative ketoreductase involved in aflatoxin biosynthesis in Aspergillus parasiticus.