Vibrio parahaemolyticus was the etiological agent in three food-related epidemics of gastroenteritis in Maryland, during August 1971. These outbreaks involved crab food products. Fifteen isolates of V. parahaemolyticus were made which included 11 from patients and 4 from foods. Serotype 04:K11 was the cause of the outbreaks. It was recovered from patients in each outbreak and gave a positive Kanagawa reaction, an indication of enteropathogenicity. Other patient isolates included types 03:K30, 03:K33, and an untypable isolate, all of which were Kanagawa negative. Food isolates included serotypes 03:K30, 02:K28, and two untypable isolates, all of which were Kanagawa negative. The outbreaks reported in this paper constitute the first confirmed foodborne epidemics due to V. parahaemolyticus in the United States. Methods for the isolation and identification of V. parahaemolyticus are presented, including a procedure for the simple conversion of conventional laboratory media into suitable culture media for this halophilic organism.