Fifty patients suffering acute bacterial diarrhea were studied under the design of single-blind randomly allocated and prospective. They received orally a single daily dose of 400 mg of lomefloxacin or trimethoprim/sulfamethoxazole 160/800 mg B.I.D. during five days. Evaluation was made in 47 patients: 23 corresponding to lomefloxacin group and 24 for the comparative preparate. Mean duration of diarrhea in the lomefloxacin group was 1.5 days vs 2.0 days in the other therapeutic group (P _ 0.001). Cultures in both groups of patients were negative after 24-48 hours post-treatment. Clinical percentage of success was 100% for lomefloxacin and 96% for those treated with trimethoprim/sulfamethozazol. Mild reactions were reported in 3 and 4 patients of each group respectively.