Isozymes from five wild-caught populations of Aedes aegypti (L.) were compared using starch gel electrophoresis to estimate rates of gene flow between and among geographically close mosquito populations. Ae. aegypti were collected from five different locations in Bangkok, Thailand. One collection was obtained from central Bangkok (Huai-Khwang); the other four samples were obtained from surrounding areas (Districts Latkrabang, Ratburana, Laksi, and Bangkok Noi). Based on 24 loci (17 enzyme systems), only minor genetic differentiation was observed between all five populations. The highest percentage of polymorphic loci (34.3) was observed from the central Bangkok population; the least percentage of polymorphism (20.0) was seen from Laksi (north Bangkok). This study indicates that a large effective migration rate exists among all five populations. No fixed genetic differences were detected.