SUMMARYMultilocus enzyme electrophoresis was used to examine genetic relationships among and between toxigenic and non-toxigenic isolates of Vibrio cholerae 01 obtained from patients and the environment in the US Gulf Coast and surrounding areas. A total of 23 toxigenic and 23 non-toxigenic strains were examined. All the toxigenic and 7 of the non-toxigenic strains had the same alleles at 16 enzyme loci, whereas the balance of the nontoxigenic strains had 9 distinct combinations of alleles. This study suggests that all of the toxigenic strains belong to a single clone, and that while some of the non-toxigenic isolates were related, most were of diverse origin.