This double-blind trial was initiated to test, in a controlled study, the value of single-day drug treatment of amebic liver abscess. Patients were treated with 2 g either of ornidazole or tinidazole, two newly developed 5-nitroimidazole derivatives, given in two equal doses during the course of 1 day. A success rate of over 94% in the 72 patients from both treatment groups who were followed up for 6 months demonstrates the efficacy of the single-day drug treatment.