Cholera epidemics occur twice a year in the endemic area of Bangladesh. Vibrio cholerae 01 can be isolated from the environment only during the epidemics and the question of possible interepidemic environmental reservoirs of V. cholerae remains open. The present laboratory-based studies investigate the role of an aquatic alga, Anabaena variabilis, as a possible reservoir. Persistence of V. cholerae inside the mucilaginous sheath of A. variabilis was observed by phase-contrast and fluorescent microscopy for more than 15 months after inoculation.