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Carbaryl (l-naphthyl N-methylcarbamate), a carbamate insecticide with a wide range of activity and relatively low degree of toxicity to animals, is one of the most commonly used pesticides. It may enter the estuarine environment as a result of run-off from agricultural lands or through its use in the control of estuarine pests. Among the various factors which determine the fate of a pesticide, microbial transformation is one of the most important. The metabolism of carbaryl by soil microorganisms has been reported (BOLLAG and LIU, 1971; LIU and BOLLAG, 1971a; LIU and BOLLAG, 1971b; BOLLAG and LIU, 1972a; KAZANO et al., 1972). It has also been shown that carbaryl is readily hydrolyzed to l-naphthol non-biologically in sea water (KARINEN et al., 1967; LAMBERTON and CLAEYS, 1970). l-Naphthol has been reported to be more toxic to fish (STEWART et al., 1967) and microorganisms (BOLLAG and LIU, 1971) than the parent compound (carbaryl); therefore, it becomes important to have information on its further transformation in order to have a comprehensive knowledge of the fate of carbaryl. The degradation of carbaryl and l-naphthol by marine microorganisms has received little attention. This investigation was undertaken to test the ability of selected species of marine bacteria, yeasts and filamentous fungi to degrade the two chemicals.