A dose range study in 18 patients suffering from intestinal amoebiasis and treated with doses of panidazole between 1.0 and 2.0 g per day for six days revealed that the best therapeutic results were obtained with the higher dose. This dose was then compared with metronidazole, at the same dose, in a clinical trial in 100 patients with intestinal amoebiasis. Cure rates were 68% and 80% for the two drugs respectively. In 100 cases of vaginal trichomoniasis treated with panidazole at the dose of 1.0 g per day for seven days in half of the patients and for 10 days in the other half, we obtained 50% and 60% cure rates. The results of our studies with both amoebiasis and trichomoniasis were not superior to those obtained with metronidazole and other nitroimidazole derivatives. Side effects were found in 74% of the patients treated for amoebiasis and in 46% of the cases treated for trichomoniasis. No toxic effects were revealed by haematological, biochemical and renal function tests nor by cardiovascular studies.