We have been utilizing members of the Drosophila paulistorum complex of semispecies to study the development of adult discriminatory behavior. In this study, three rearing methods were used to examine the effects of previous exposure to heterosemispecifics on reproductive isolation among the various semispecies. Experimental flies were exposed to heterosemispecifics by one of three methods: exposure to airborne heterosemispecific stimuli from egg through sexual maturity, physical contact with heterosemispecifics only during the postimaginal period, and mixed culturing (total physical contact with heterosemispecific individuals during each of five preimaginal stages). Effects of the first treatment varied with semispecies. The second treatment had no significant effect on mating behavior. The third treatment of mixed culturing reinforced sexual isolation.