Fifty-seven new O serogroups have been added to the existing serotyping scheme of Vibrio cholerae to extend the scheme from O84 to O140. Prominent new additions were serogroups O139 and O140. The reference strain of O139 was isolated from a patient from an epidemic of cholera-like diarrhea in Madras, Southern India. Serogroup O140 was assigned to a group of V; cholerae strains which were tentatively named as the ''Hakata'' serogroup and which possessed the C (Inaba) factor but not the B (Ogawa) nor the A (major specific antigen of O1 serogroup of V. cholerae). As all antisera against reference strains of V; cholerae contained some amount of antibody to the rough (R) antigen, all diagnostic O antisera must be absorbed with the reference rough strain, CA385.