In Argentina, reinfestation with Aedes aegypti was registered in 1986. At present, the mosquito is well established in 10 provinces, from Buenos Aires up to the country's northern frontiers. This paper presents estimates of genetic variability in Ae. aegypti populations from central Argentina and determinations of genetic distances among them. We analyzed allozymic frequencies at 11 loci in samples from 3 localities. The proportion of polymorphic loci varied between 27.3 and 63.6. Expected mean heterozygosity ranged from 0.090 to 0.161 and Rogers' similarity among samples ranged between 0.909 and 0.958. The lack of relationship between genetic and geographic distances is in agreement with a recent colonization of the studied area. The mean Wright's coefficient FST value (0.065) indicates low levels of genetic differentiation among populations from different localities. Given the recent reinfestation with this mosquito in Argentina, the high levels of polymorphism found could indicate multiple introductions of representative samples from genetically different subpopulations.