We have identified and studied the chromosomal location of the human Rieske Fe-S protein-encoding gene UQCRFS1. Mapping by hybridization to a panel of monochromosomal hybrid cell lines indicated that a UQCRFS1 partial cDNA was derived from either chromosome 19 or 22. By screening a human chromosome 19 specific genomic cosmid library with a probe from this cDNA sequence, we identified a corresponding cosmid. Portions of this cosmid were sequenced directly. The exon, exon:intron junction and flanking sequences verified that this cosmid contains the genomic locus. Fluorescent in situ hybridization (FISH) was performed to localize this cosmid to chromosome band 19q12.