We have adapted Aedes aegypti cells to Eagle's minimal medium containing nonessential amino acids, glutamine, and 5% fetal bovine serum. In this medium, cells maintained at 28°C under a 5% CO2 atmosphere had a doubling time of 42 hr. Ninety-three percent of the cells in a typical population contained 6 full-size chromosomes and an apparent chromosome fragment. Ae. aegypti cells could be distinguished from Ae. albopictus cells by the sizes of the small heat shock proteins, whose synthesis was induced by a brief treatment at 41°C. Analysis of the small heat shock proteins synthesized by dissected ovaries from Ae. aegypti and Ae. albopictus confirmed the species of origin of the 2 cell lines.