During the cholera epidemic in 1973, nine contact carriers of Vibrio cholerae El Tor serotype Ogawa were identified in a family from Naples as well as six others coming from different parts of the city or its surroundings. All the subjects were admitted to the quarantine ward of the ‘Cotugno Hospital’ (Naples) in which they remained continuously for 14 or 16 days. During this time these bacteriologically confirmed carriers were treated orally with a long-acting sulphonamide (sulphamethoxypyrazine, Kelfizine). Coprocultural examinations carried out on each patient on average 7 times after the treatment over a period of 6 months, proved the absence of V. cholerae. Serological tests also showed high levels of agglutinating and vibriocidal anticholera Ogawa antibodies in two unvaccinated carri