Populations of Aedes aegypti were collected in 1976 and 1979 from a number of different areas of New Orleans and analyzed for genetic variation of 12 isozyme loci. Although six loci were polymorphic, the majority of loci showed no significant genetic differentiation over time or between regions. The greatest amount of genetic differentiation was found between populations bordering the Mississippi River and the two inland areas, Mid-City and Mount Olivet. The low amount of genetic heterogeneity among areas is consistent with the known rapid spread and migration of A. aegypti in recent years. New Orleans A. aegypti are genetically most closely related to populations from Florida, and are less related to collections from several Caribbean islands with a recent history of epidemic dengue fever.5 Knowledge of the structure of A. aegypti populations in New Orleans, as well as their genetic relatedness to those of other regions, may provide important information concerning the potential of these populations as vectors of epidemic dengue fever.