On pyrethroid and four organophosphorus (OP) insecticides were evaluated as contact aerosols in wind tunnel tests against adult Toxorhynchites rutilus rutilus (Coquillett). The data indicate that Tx. r. rutilus and Culex quinquefasciatus Say were not significantly different in susceptibility to malathion (0,0-dimethyl phosphorodithioate of diethyl mercaptosuccinate), fenthion (0,0-dimethyl 0-[4-(methylthio)-m-tolyl] phosphorothioate), naled (1,2-dibromo-2,2-dichloroethyl dimethyl phosphate), and chlorpyrifos (0,0-diethyl 0-(3,5,6-trichloro-2-pyridyl) phosphorothioate). Resmethrin [5 (phenylmethyl)-3-furanyl] methyl 2,2-dimethyl-3-(2-methyl-1-propenyl)cyclo propanecarboxylate (approx. 70% trans, 30% Cis-isomers)) was ca. 1.4X more toxic to C. quinquefasciatus than to Tx. rutilus. Aedes aegypti (L.) was ca. 2X more susceptible than Tx. r. rutilus to 3 of the 4 OP's tested and ca. 16X more susceptible to resmethrin. Chlorpyrifos was equally toxic to Ae. aegypti and Tx. r. rutilus. Male and female Tx. r. rutilus did not differ significantly in their response to the insecticides tested.