Freely behaving Aplysia californica can learn that food is inedible. Animals were given access to seaweed tied into canvas and attached to a force transducer. Animals repeatedly found the stimulus, attempted to ingest it, and failed. The force transducer provided an objective record of the number of attempts made by the animal to ingest the stimulus, the length of each attempt, and its intensity (i.e., peak force exerted). Within 2.5 hr, animals showed significant declines in these 3 measures of response to the stimulus. When exposed to the same stimulus the next day, animals showed more rapid declines in responsiveness, which indicate a retention of learning. Training appeared to be specific: Responses to the seaweed Laurencia of animals previously trained on the seaweed Ulva do not differ from the responses of naive animals to Laurencia.