Mature mosquito larvae of Aedes communis (De Geer) were collected from woodland pools and treated in solutions of 32P. Adults from these larvae were captured using 20 traps employing battery operated lights, and dry ice producing CO2. Trapping was continued for 13 weeks, and a total of 31 radioactive flies were captured during the period. The majority of the radioactive mosquitoes were recovered at the outer limits of the study area of 1 mile, most of them east and south from the release point, and the last tagged individual was trapped 44 days after emergence. Thus, it seems probable that most of the tagged mosquitoes dispersed further than the limits of our study area and that they survived for more than 1 month in the field.