Using underwater television, photography, and fish traps the attractiveness of a number of natural baits and pure compounds to four species of marine fish was examined directly in their natural habitat. Winter flounders (Pseudopleuronectes americanus), mummichog (Fundulus heteroclitus), and Atlantic silversides (Menidia menidia) were each attracted by specific amino acids. Only flounders and killifish exhibited biting and digging behavior in the vicinity of the odor source. Hagfish (Myxine glutinosa) could be trapped using a variety of natural baits but no single amino acid or a variety of combinations of amino acids or amines was effective. The active principle(s) in cod muscle accounting for its attractiveness to hagfish was found to be heat stable, of small molecular weight and extractable with ethanol. Chromatographic separation of the ethanol extract resulted in only one active fraction consisting of several compounds. This fraction, however, accounted for only a small amount of the total activity in the ethanol extract, suggesting a multicomponent system.