The status of susceptibility to malathion of wild-caught Aedes sollicitans and their F1 progenies from 5 areas in New Jersey was determined by topical application. Laboratory strains of this species from Louisiana and Texas, established in 1981, exhibit baseline susceptibility (LD50s 2.1 ng/male, 3.4 ng/female, 3.4 ng female Louisiana; 2.3 ng/male, 3.6 ng/female Texas). However, in all New Jersey populations tested, a plateau in their respective log dosage-probit lines is distinguishable suggesting incipient resistance to malathion. The relationship between topical application data and malathion aerial ULV space sprays is discussed.