We have purified bleomycin hydrolase from yeast (molecular mass 55,000 Da). Using protein sequence-derived degenerate oligonucleotide primers and amplification by polymerase chain reaction, the yeast gene BLH1 was isolated and characterized. The deduced amino acid sequence (483 amino acids) exhibits surprisingly high homology to vertebrate bleomycin hydrolase (43% identical residues and 22% conserved exchanges). It contains three blocks of sequences found conserved in other members of the thiol proteinase family and thought to be associated with the catalytic centre. BLH1 is non-essential under all growth conditions tested. However, in the presence of 3.5 mg bleomycin/ml medium wild-type cells have a slight growth advantage compared to blh1 mutant cells.