It has been hypothesized that Vibrio cholerae is an autochthonous flora of the estuarine and brackish water environment. Zooplankton and phytoplankton have been considered as possible reservoirs. The present study was carried out in microcosms to confirm the role of a cyanobacterium, Anabaena sp., as a reservoir of V. cholerae O1 using culture, polymerase chain reaction (PCR) and immunoelectron microscopy. Survival of culturable V. cholerae in microcosms was monitored by using tellurite taurocholate gelatin agar. Culturable V. cholerae were detected for up to 1 h in association with Anabaena sp. from a microcosm. However, viable but nonculturable (VBNC) V. cholerae O1 were detected for up to 25 months using PCR and immunoelectron microscopy. Results also showed that VBNC V. cholerae can multiply and maintain their progeny in the mucilaginous sheath of Anabaena sp. This is the first time that PCR and immunoelectron microscopy have been used to detect nonculturable V. cholerae in association with Anabaena sp. This study further clarifies the role of Anabaena sp. as a possible reservoir of cholera.