A controlled field study of the treatment of cholera carriers is described. The households of cholera patients were assigned to two groups: one group received 2 doses of tetracycline daily for 3 days and the other received a placebo of multivitamins. From the second to the fifth day of follow-up, there was a significant decrease in the number of vibrio excretors in the treated group as compared with the placebo group. Soon after withdrawal of the drug, the number of excretors rose in the treated group and ultimately it was the same in both groups.