The dispersal of the tule mosquito, Culex erythrothorax, was studied in the proximity of LakeTynan in the city of Watsonville, CA. From July l8 to 20,2OOO, approximately 43,000 female Cx. erythrothoraxwere marked with luminous powder and released, using a distinct color each day. Recaptures were .sampled byusing 2l carbon dioxide-baited traps ranging in distance from zero to 2.8 km from the release site. Duiing thl5 days of postrelease sampling,3lg marked mosquitoes were recaptured. The percentage of the marked mosquitoesthat were recaptured was 0.46, 0.50, and 0.55% based on the 3 releises, respectively. Overall, themosquitoes dispersed 0.57 km/day; the mean distance traveled increased during the 5-day sampling period fromo.42 krn/day to 0.89 km/day from day I to day 5, respectively. Based on the Lincoln index, the eitimated totalpopulation size for Cx. erythrothorax in the study area ranged from 3.8 to 9.4 million mosquitoes. This specieswas found to constitute a nuisance to local residents because of the abundance of this speciLs and its capibilityto disperse into proximal communities.