A clinical trial of praziquantel was carried out in patients with opisthorchiasis using low dosages with 30 and 60 days follow-up. In group III, 30 patients treated with praziquantel 25 mg per kg body weight bid, for one day yielded a cure rate of 88%. In group IV, 12 patients received 25 mg per kg body weight in a single dose and gave a cure rate of 44 %. In group V, 55 patients received 40 mg per kg body weight in a single dose and yielded a cure rate of 91%. Mild and transient side effects were present in 54%, these included abdominal pain, lassitude, headache, dizziness, nausea, diarrhoea, myalgia and tachycardia. Clinical improvement was observed in most of the patients after one month and 33% of them were clinically cured in two months. The recommended dose of praziquantel for the treatment and control of opisthorchiasis in the endemic area is a single dose of 40 mg per kg body weight after meals.