Two esterase loci, Est-4 and Est-5, in Aedes albopictus encode carboxylesterases in 4th-instar larvae, pupae and adults. The electrophoretic bands migrate on agar gels toward the most anodal side, those of Est-5 followed by those of Est-4. Linkage studies on the two loci revealed that they were arranged on linkage group 2 in the following order: Est-4-(0.9 +/- 0.7 to 4.3 +/- 1.4 map units)-p(pigmented pupa)-(2 map units, as previously determined)-Wb(White-body)-(18.2 +/- 2.6 to 21.0 +/- 1.8 map units)-Idh-2(isocitrate dehydrogenase-2)-(13 map units, as previously determined)-alpha-Gpdh(alpha-glycerophosphate dehydrogenase)-(9.0 +/- 1.8 to 19.9 +/- 3.1 map units)-Est-5. The esterase loci were compared with those reported in other Aedes species with respect to their linkage homology.