The protein, choline acetyltransferase (ChAT; EC 2.3.1.6), was analyzed in wild-type and two different temperature-sensitive ChAT mutants of Drosophila (Cha(ts1) and Cha(ts2)) using newly generated monoclonal antibodies. In all of the three genotypes, Western blots of crude fly head extracts showed a band stained at approximately the 80-kDa position, supporting the hypothesis that these temperature-sensitive mutants were generated by point mutation in the structural gene. The staining intensity of the bands indicated that these mutants have a lesser amount of ChAT protein than wild-type, even when they are reared at the permissive temperature (18 degrees C).