Between 1972 and March 1977, 367 cultures of Yersinia enterocolitica were examined for biotypic and serotypic characteristics by Plague Branch, Vector-Borne Diseases Division, Center for Disease Control. Standard biotyping tests were performed. Serotyping antisera used contained somatic serofactors 1 through 9, 11 through 21, 24, 32, and two new types designated 'Arizona' and 'Tacoma'. The cultures examined included 68 from human illnesses; 43 from 12 species of vertebrate and invertebrate animals; 43 from raw meats, milk, or seafood; and 215 from 154 different water samples. Geographic origins of the cultures included 16 states of the USA and four provinces of Canada.