The objective of this study was to determine esterase enzyme polymorphism in 16 natural Musca domestica L. populations from the Aegean and Mediterranean regions of Turkey by using the native polyacrylamide gel electrophoresis (PAGE) technique. The high level of genetic variation among populations and species make esterase enzymes an important tool for analyzing genetic differentiation and evolutionary relationships in insects. In the present study, 22 a-esterase bands were detected by using a-naphthylacetate as a substrate. The frequencies of these bands were variable within and among populations. Neither regional nor population specific esterase bands were detected. The origin of speciation of M. domestica is unknown, but the southern Palearctic region, particularly the Middle East, has been suggested as the likely candidate location. Studies on genetic diversity in M. domestica are important for providing knowledge that will better enable us to understand the origin of this species. This preliminary study is important because it is the first in the literature to illustrate the esterase isozymes and their frequencies for this part of the world. For a better evaluation and understanding of the ongoing situation of M. domestica populations in Turkey as a Palearctic country, however, further research is needed to screen not only populations from these 2 regions but also from other regions for many other enzyme and DNA loci.