Choline acetyltransferase (CHAT) (EC 2.3.1.6) is the biosynthetic enzyme for the neurotransmitter acetylcholine in the central and peripheral nervous systems. In this study, a human CHAT genomic clone has been isolated and partially sequenced at its 5' end. This fragment contains the first four exons with an ACG initiator codon and potential control regions including TATA, CAAT, GC boxes, and several transcription control sequences. A comparison of the primary structure of CHAT among pig, rat, mouse, and Drosophila is presented.