An ether resistant (Eth-29) and a sensitive (bw; st; svⁿ) strains were examined for their sensitivity to halothane. Adult flies of one day old were exposed to halothane for a given time and mortalities were assessed one day later. The Eth-29 strain was found to be more resistant to halothane than the bw; st; svⁿ strain. It was unusual that the males of the Eth-29 strain showed more resistant than the females, although the situation was reversed in the bw; st; svⁿ strain. Genetical analyses revealed that the resistance to halothane was an incompletely dominant trait, maternal effect was negligible and that the major gene(s) with respect to halothane resistance was located on the third chromosome and the minor genes were on the X and second chromosomes. It will be discussed whether the genetical basis of the halothane resistance differ from those of the ether and chloroform resistances reported previously.