Many physicochemical factors affect the survival of Vibrio cholerae in the aquatic environment. An attempt was made to study the combined effect of pH and iron on the survival of V. cholerae in water in a laboratory environment. None of the 6 strains of V. cholerae used survived at pH 5.0; survival of all strains increased with increasing pH. The effect of ferric oxide on survival was significant for V. cholerae O1 only, not for non O1 strains. The longest survival of V. cholerae non O1 was 82 d, of El Tor V. cholerae 68 d, and of classical V. cholerae 56 d.