Aedes caspius Pallas populations from the Mediterranean regions are genetically highly polymorphic, and may diverge into 2 genetically isolated forms. We examined the genetic structure of 3 mosquito populations from Faiyum oasis, using starch gel electrophoresis at 8 gene loci, from which only one was monomorphic. Genetic variability was high (A = 1.97; H = 0.12; P = 54.2, 66.7). Eleven out of 16 population--enzyme combinations with variability exhibited heterozygote deficiency from Hardy--Weinberg expectations. These results suggest that tested populations represent a mosquito complex, although no genetic divergence was detected (D = 0.012) since presumed sympatric gamodemes were sampled as a single population. It is of prime importance to detect cryptic gamodemes and to elucidate the present status of Ae. caspius, as this may greatly influence control strategies.