The ability of oral antibiotic treatment to control diabetic diarrhea was documented by a double-blind study involving a patient with this condition. When the patient was given Mysteclin-F, the diarrhea subsided promptly, only to recur when a placebo was substituted,. The erratic behavior of diabetic diarrhea is indicated, however, by the fact that a remission eventually occurred, and no further treatment was required. Although not all patients with diabetic diarrhea respond to antibiotic treatment, its trial merits consideration forthose patients who are refractory to the simpler forms of treatment.