Recombinant clones from a cDNA library of an Aphanocladium album chitinase-overproducing mutant strain were isolated by screening with antiserum against a 39 kDa chitinase purified from this hyperparasitic fungus. Analysis of the isolated positive clones indicated that most of them carried the same cDNA. A cDNA from this group was used as a hybridization probe to isolate an 8 kb DNA fragment from a genomic library of the wild-type strain. The chitinase 1 gene was mapped to this fragment by two independent approaches. Its partial DNA sequence was in perfect agreement with an amino-terminal peptide sequence obtained by sequencing 23 amino acids of the 39 kDa chitinase. Its transfer in Fusarium oxysporum resulted in a transformant producing both a protein of about 39 kDa that cross-reacted with the chitinase antiserum and a chitinase activity that was inhibited by the same antiserum. Northern blot analysis indicates that the cloned chitinase gene was subject to catabolite repression and appeared inducible by chitin.