A Drosophila cDNA homologous to a rat tyrosine hydroxylase (TH) probe has been isolated and sequenced. The deduced amino acid sequence predicts a 57,861 dalton protein with almost 50% identity with rat TH. In vitro transcription of the cDNA followed by in vitro translation yields a single protein species of approximately 58,000 daltons. The in vitro translation product, as well as a protein of the same molecular weight from wild-type Drosophila head protein extracts, is recognized by an antibody made against bovine TH. The presence of TH enzymatic activity in heads was demonstrated. In situ hybridization to polytene chromosomes localized the gene to 65B. The comapping of the mutant pale to this same region, as well as its phenotype, suggests that pale may be a TH mutation.