The dynamics of heterospecific and conspecific mating between Florida strains of Aedes aegypti and Aedes albopictus was examined. In nonchoice experiments where conspecific males were not available, dissection of the spermathecae showed that heterospecific insemination was an infrequent event for both species combinations (10.6% for Ae. albopictus with Ae. aegypti males, 3.6% for the reciprocal cross). Few eggs were produced from heterospecific crosses and all were nonviable. Frequency of heterospecific mating was not increased when the hindtarsi of females were removed, eliminating a significant mechanism for fending off unwanted courtship. When held with males of both species, females mated with conspecifics and oviposited without regard to the presence of heterospecifics. In low density experiments, a single female of either species caged with an excess of heterospecific males, the conspecific male always located and inseminated the female. These results indicate that significant prezygotic and postzygotic reproductive isolation exists between Ae. aegypti and Ae. albopictus.