Vibrio cholerae was isolated at several locations in Chesapeake Bay in fall 1976 and spring 1977. Strains induced fluid accumulation in rabbit ileal loops and positive activity in Y-1 adrenal cells. Vibrio cholerae, Vibrio parahaemolyticus, and related vibrios show a spatial and temporal distribution characteristic of Vibrio species in an estuary. The Vibrio cholerae strains isolated from Chesapeake Bay represent serotypes other than O-group I—that is, so-called nonagglutinable vibrios—and are not recognized as a serious epidemic threat, although they have caused choleralike diarrhea sporadically.