Cholera has been reported in the state of Orissa, India during the past decades. An outbreak of diarrheal disease occurred during November 1 to November 9, 2000 in Rusi- pada village near Puri, which was inhabited by a population of approximately 560. During the outbreak, Vibrio cholerae O139 strains were isolated from clinical specimens collected from patients with acute diarrhea admitted to the infectious diseases (ID) hospital in Puri and from environmental samples collected from multiple bodies of water in the village. The index case with acute diarrhea was a 60-year-old female resident of Rusipada who had not visited any known out- break-related areas, including an outbreak 1 week prior to her symptom onset in a nearby village. All the isolated strains were positive for ctxA, tcpA, ace, and zot genes, produced cholera toxin, and exhibited a similar antibiogram pattern. Comparison of DNA fingerprinting analysis by randomly am- plified polymorphic DNA (RAPD) and pulsed-field gel elec- trophoresis (PFGE) method and dendrogram constructed from RAPD revealed that genetic homogeneity exist between the clinical and environmental O139 strains. Epidemic and endemic cholera is a major public health problem in many developing countries and continues to be an important cause of morbidity in many areas of Asia, Africa, and Latin America. Among more than 200 serogroups of V. cholerae so far identified,1 only O1 and recently identified O139 serogroup2-5 are capable of causing epidemic cholera. It is now widely accepted that O139 Bengal like O1 and non-1 and non-O139 Vibrio may survive better in aquatic environ- ments6-8 and environmental water is the reservoir for infec- tious V. cholerae.7,9 In this report we investigated the clonal relationship between strains of V. cholerae collected both from stool specimens from persons with acute diarrhea and from environmental sources of water. During the outbreak of diarrhea, 23 non-randomly selected rectal swabs were col- lected from the hospitalized diarrhea patients in ID hospital, Puri in Cary-Blair Transport (CBT, DIFCO,USA) medium and transported to the Microbiology Department of Regional Medical Research Centre (RMRC), Bhubaneswar and bacte- riologically analyzed following standard technique.10 Subse- quently after the isolation of V. cholerae O139 as the etiologi- cal agent of the outbreak, 20 water samples non-randomly selected were collected from water bodies situated at various distances in that village to determine the source of contami- nation following a previous method.11 Presumptive identifi- cation of 10 and 6 V. cholerae were isolated from rectal swabs and water samples respectively and the strains were aggluti- nated with monoclonal O139 antiserum supplied by NICED, Kolkata, India and were confirmed to belong to V. cholerae serogroup O139. To investigate the similarities of clinical and environmental strains of V cholerae O139, drug susceptibility test, cholera toxin assay, detection of virulent genes by polymerase chain reaction (PCR) assay, RAPD finger printing assay, and PFGE were performed. A monosialoganglioside (GM1) enzyme-linked immuno- sorbent assay (ELISA) was used to examine cholera toxin production in V. cholerae O139 strains by the method Sven- nerholm and Holmgren.12 Drug susceptibility test was per- formed following the method described elsewhere,13 with the antibiotics (Hi-media Laboratories, Bombay, India) ampicil- lin (A, 10 g), chloramphenicol (C, 30 g), co-trimoxazole (Co, 25 g), ciprofloxacin (Cf, 5 g), furazolidone (fz, 100 g), gentamicin (G, 10 g), neomycin (N, 30 g), nalidixic acid (Na, 30 g), norfloxacin (Nx, 10 g), streptomycin (S, 10 g) and tetracycline (T, 30 g). Characterization of strains as sus- ceptible or resistant was based on size of the inhibition zone around each disc according to manufacturer's instructions, which matched interpretive criteria recommended by the WHO.14 Strains showing an intermediate zone of inhibition were interpreted as resistant to that drug on the basis of pre- vious MIC studies conducted with V. cholerae.15