Wing length and protein content were compared in individual specimens of male and nonbloodfed, nongravid female mosquitoes. The following groups were tested: field-collected and colonized Aedes aegypti, field-collected Culex nigripalpus and Aedes vexans, and colonized Culex quinquefasciatus and Psorophora columbiae. The correlation coefficient varied from 0.91 in Ae. aegypti males to 0.98 in Ae. vexans females, and in each group the P value was less than 0.001. This close correlation suggests that both wing length and protein measurement are reliable expressions of size in adult mosquitoes.