The authors present the results of trials carried out with trichlorophenol piperazine (C-416) in the treatment of Ascaris lumbricoides, Ancylostomidae and Trichuris trichiura infections. Several therapeutic schedules were tried in order to evaluate tolerance and efficacy of the drug. CI-416 proved to be a valuable antihelmintic in the treatment of Ascaris lumbricoides and hookworms, specially when given in doses of 2-3 g daily for 4 days and 50 and 80 mg/kg/body weight daily for 3 to 4 days. Good results were obtained with a single dose of 3-5 g, specially regarding the worm burden reduction. Tolerance to the drug was relatively good; none therapeutic course had to be interrupted even with daily doses of 80-100 mg/kg/body weight.