Ampicillin trihydrate, administered orally, significantly shortened the duration of diarrhea, abdominal cramps, and fever in 30 adults with shigellosis, when compared to the duration of these symptoms in 30 nontreated controls. Ampicillin also effectively eliminated shigallae from the intestinal tract within 24 to 48 hours of therapy in a majority of cases. In contrast, kanamycin sulfate, given parenterally, was not effective in altering the clinical course, nor in decreasing the number of patients excreting shigellae. Thirty percent (9) of patients treated with ampicillin and 40% (24) in both the kanamycin and control groups continued to shed shigellae 12 days after the start of antibiotic therapy. Although ampicillin therapy effectively shortened the clinical course of shigellosis, further studies are needed to determine whether convalescent excretion of shigellae can be eliminated with either higher doses or a longer course of antibiotic therapy.