We have isolated a human cDNA clone homologous to fungal ERG3, a gene encoding sterol C-5 desaturase. The full nucleotide sequence of this human cDNA revealed a 708-bp open reading frame that encodes a 236-amino-acid polypeptide. The gene was expressed in all normal human tissues examined. We determined its location to chromosome 11q23.3 by fluorescence in situ hybridization.