Spermatogenic normaI males of Drosophila melanogaster were fed with 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin, 2, 3, 4, 7, 8-pentachloro-dibenzofuran or 1, 2, 3, 4, 7, 8-hexachloro-dibenzofurans and subsequently mated to the Muller-5 females to detect recessive, lethal mutations occurring in the X chromosome. Some mutants were obtained in particular in the brood A, in which the chemical affected probably at the maturation stage of spermatogenesis. However, the mutation rates in total were scarcely larger than the control. In the F_1 of the treated flies hatchability and pupation rates were again not different from the control. On the other hand, some of the treated males gave F_1 with developmental abnormality, in which neither eggs nor pupae appeared. Moreover, the treatment induced several malformed individuals which lacked half of the thorax or had a hollow eye.