Previous studies have demonstrated the value of purging in detecting inapparent cholera infection, but the technique has not been generally accepted. The present study shows that the method can be recommended as a routine procedure to determine when convalescent cholera patients should be discharged from hospital. It may also be useful in detecting carriers of Vibrio cholerae and for evaluating chemotherapy. In this study, five of the eight patients who excreted vibrios after purging had been treated with 2 g of chloramphenicol daily for three days, a finding that throws doubt on the adequacy of this treatment. Purging with magnesium sulfate is simple, well tolerated and ideal for hospitalized patients or for subjects whose stools can be promptly cultured. Since magnesium sulfate is inhibitory to Vibrio cholerae, this purgative is not well suited for field studies, where there may be delays in culturing.