Malathion ULV applied by airplane over the city of San Juan, Puerto Rico in 1978 was ineffective against Aedes aegypti as shown by the percentage of infested cement vases and the number of larvae and pupae in a large cemetery before and after treatment. Malathion ULV applied by LECO Fog Generators mounted on vehicles was also ineffective in 1979 against adults as shown by landing counts in a residential area before and after several treatments. The number of cases of dengue reported in 1977 and 1978 are listed with reasons for not giving much weight to such data in evaluating Ae. aegypti control programs in Puerto Rico.