A recessive male-specific lethal mutant of Drosophila melanogaster is described. The mutant, mle(3) 132, which is the first to be described on the third chromosome, is located at 3-25.8. Homozygous males show delayed development and die during the larval stages. The mutant shows no interactions with sex-transformation mutants, tra-2, tra-2^OTF, tra, or dsx: thus only single-X individuals are killed regardless of the phenotypic sex.