Sulfadoxine, a long-acting sulfonamide, and tetracycline were compared as regards their effectiveness in reducing transmission of cholera infection among the contacts of cholera patients in Calcutta. A total of 109 healthy family contacts of confirmed hospitalized cholera patients were treated with a single oral dose of sulfadoxine graded according to age. Another similar group of 101 contacts received 6 divided doses of oral tetracycline over a period of 3 days. All these contacts were bacteriologically examined for 15 days. Results showed that tetracycline was effective in significantly reducing the load of cholera infection from the 2nd to 6th day, while sulfadoxine was effective from the 3rd to the 6th day. The advantages and disadvantages of the two drugs as chemoprophylactic agents in cholera are discussed.