Interactions among 3 sex-specific lethals, da, Sxlf#1 and mle(3)132 of D. melanogaster were studied as to the effects on viability and sex transformation. Six crosses involving these mutants were made. The mle(3)132 interacts with the da-Sxl system both maternally and zygotically. These 2 effects are opposite in action. Maternal mle(3)132 enhances both lethal and sex transforming actions of the da-Sxl system. Zygotic mle(3)132, on the contrary, suppresses the lethal action. Roles of these 3 sex-specific lethals are discussed in relation to sex determination and dosage compensation.