Eight experimental pyrethroids, DDT, lindane and malathion were compared for effectiveness against laboratory colonies of insecticide-susceptible and DDT-insecticide-resistant strains and a field collected strain of Anopheles quadrimaculatus, a laboratory colony of Aedes taeniorhynchus, and a field-collected strain of Psorophora columbiae. In the initial laboratory evaluation against Ae. taeniorhynchus the pyrethroids were from 5X to 29X more effective than malathion. The pyrethroids were less effective against the DDT-resistant strain of An. quadrimaculatus than against the insecticide-susceptible strain. Against the field strain, they were intermediate in effectiveness. The pyrethroids were from 7 to 139X more effective than malathion against Ps. columbiae. The LC50 value of malathion against the field strain An. quadrimaculatus was 26X greater that the value found in 1980 and 50X greater than the value found in 1978.