A study was carried out in 80 patients with acute intestinal amoebiasis to compare the efficacy of treatment with a single oral dose of 2 g secnidazole and a 5-day course of 750 mg tetracycline plus 1 g clioquinol per day. Patients were allocated at random into one or other treatment group and returned for clinical assessment and microscopic examination of stools for the presence of the trophozoite or haematophagous form of Entamoeba histolytica on Days 1 to 7, 14, 21 and 28. The results showed that secnidazole produced significantly faster and more effective treatment than tetracycline/clioquinol. At the end of the follow-up period, 7 of the 40 patients in the tetracycline/clioquinol group were classified as 'parasitological' failures but there were none in the secnidazole group. Moreover, there were no cases of relapse or persistence of clinical signs in the secnidazole-treated patients. Both treatments were well tolerated.