A controlled comparison of furazolidone and tetracycline in the treatment of cholera indicates that, in either dosage used, furazolidone reduced total stool volume by 50% and duration of diarrhoea by 40%. These results are comparable to those achieved with tetracycline, which was given in presently recommended dosage. Both furazolidone and tetracycline significantly reduced the rate of stool output within 18 to 24 hours of starting antibiotic treatment. Furazolidone was significantly less effective than tetracycline in rapidly and consistently terminating vibrio excretion. One convalescent carrier of cholera vibrios was identified among control patients; none was identified among patients treated with either tetracycline or furazolidone. All Vibrio cholerae strains tested were sensitive to tetracycline and furazolidone, but larger concentrations of the latter were required to achieve inhibition of growth. It is concluded that tetracycline remains the antibiotic of choice in cholera but that furazolidone would be a useful adjunct to cholera therapy when tetracycline is unobtainable or if strains of V. cholerae with clinically significant resistance to tetracycline should be encountered.