Dadisman, T. A., Jr. (Epidemiology Program, CDC, Atlanta, Ga. 30333), R. Nelson, J. R. Molenda and H. J. Garber. Vibrio parahaemolyticus gastroenteritis in Maryland. I. Clinical and epidemiologic aspects. Am J Epidemiol 96: 414–426, 1972.—During August 1971, three food-borne disease outbreaks caused by the bacterium V. parahaemolyticus occurred in Maryland. In two of these instances, steamed crabs were the vehicle of infection, and in the third, crab salad prepared from canned crabmeat. The outbreaks involved about 425 ill persons (57.0%) of an estimated 745 at risk. Incubation periods were between 13 and 23 hours. Symptoms of illness were severe diarrhea, abdominal cramps, nausea, vomiting, headache, chills and mild fever, persisting between one and five days. There were no deaths. In each outbreak, the organism was recovered from the stools of ill persons, and from crabs and crabmeat. The steamed crabs became contaminated after cooking, most likely while being transported and stored with live crabs. The processed crabmeat was probably contaminated while being picked and canned. V. parahaemolyticus has been found in United States coastal waters, sediment, fish, and shellfish, but documentation of its role in causing human gastroenteritis in this country has not been previously reported. The organism is the cause of many foodborne outbreaks in Japan.