Cholera carrier studies have been in progress in Calcutta since April 1966, in areas of high endemicity with a population of about 13 000. Carriers are traced through periodic examinations of samples from latrines, users of vibrio-positive latrines, contacts of cases of cholera and apparently healthy persons.The latrine survey showed that 46.2% of the latrines were infected, and brought 54 carriers to light; the over-all carrier rate in the study area was estimated as 1.3%. The carrier rate among household and family contacts of hospital cases of cholera was 1.6%. None of the contacts of 9 persons with choleraic diarrhoea was positive. Vibrios were also isolated from water and flies near positive latrines.The results indicate that carriers can occur even in the absence of overt disease, that infection persists in many households, and that carriers may transmit the infection.