A severe epidemic of dysentery began late in 1979 in northeast Zaire and spread to Rwanda, Burundi, and Tanzania. The epidemic strain is a multiply resistant Shigella dysenteriae type 1, which acquired resistance against trimethoprim and more recently against nalidixic acid in the course of the epidemic. A comparative open trial in Rwandan adults with Shiga dysentery involved 18 patients treated with norfloxacin at 400 mg twice daily and 12 patients treated with nalidixic acid at 1 g three times daily for 5 days. All isolates showed in vitro susceptibility to both drugs. Though norfloxacin eliminated Shigella organisms from stools more rapidly than nalidixic acid, its clinical superiority did not reach the level of significance. Norfloxacin is a promising drug and is more effective than nalidixic acid in the treatment of multiresistant shigellosis.