Abstract
Male hybrids from Mesitas and Santa Marta (Colombia) strains of Drosophila paulistorum are sterile. Homogenates of males belonging to these strains and from the hybrids were injected into Mesitas or Santa Marta females, which were crossed to males of their own strains, so that their progenies were genetically nonhybrid. Nevertheless, some of the males from these progenies were sterile. Male progenies of females that were injected with homogenates from males that disagreed in the source of cytoplasm with the recipients were sterile. No sterility was induced if the donors and the recipients had similar cytoplasm.