The ability of 149 benzyl and cinnamyl substituted phenol and 1,3-benzodioxole derivatives to affect the growth and development of immature mosquitoes was assessed in the laboratory. Several of the more active compounds were also evaluated in small field plots. Nineteen of the materials that were most effective, with LC-90's of 0.1 ppm or less against Anopheles quadrimaculatus, were also assessed against Anopheles albimanus and Aedes taeniorhynchus. In the laboratory and field, the more active compounds in this group of insect growth regulators were similar in effectiveness to the previously reported 2,6-di-tert-butyl-4-(a,a-dimethyl benzyl (MON-0585).