A single dose of Tetramisole, 2.5 mg/kg body weight, was given to the infected cases of intestinal parasites. The number of cases were: Ascaris lumbriocides 96, hookworm 16, Trichostrongylus orientalis 10, Trichocephalus trichiurus 114 and Clonorchis sinensis 19. No dietary restriction before and after the administration of Tetramisole was required. 1. In Ascaris infection the egg negative conversion rate and the egg reduction rate were 92.7 per cent and 99.5 per cent, respectively. 2. In Trichostrongylus orientalis infections, 9 out of 10 cases were resulted egg negative after the single dose of Tetramisole, and hookworm, 12 out of 16 administered showed egg negative. However, there were no appreciable effectiveness to the cases of Trichocephalus trichiurus and Clonorchis sinensis. 3. Mild and transient side effects were noted in 75 cases (54.5%) out of 140 cases. The main symptoms were dizziness (25.5%), anorexia (25.5%), abdominal pain (18.6%), diarrhea (16.6%), headache (15.2%), nausea (14.4%) and fever (11.0%). From the above results, it is anticipated that Tetramisole is an effective anthelminthic for elimination of Ascaris, Trichostrongylus and hookworm.