Single doses of piperazine citrate were administered during mass treatment of human ascariasis in five study areas in the mountains of eastern Kentucky. A total of 282 persons was treated in four groups with three different dosage schedules, two groups receiving a laxative after treatment. In the more successful laxative group, 64 per cent of the individuals had egg counts reduced to zero as determined by observations before and after treatment. However, in another group omitting the laxative, a cure rate of 79 per cent was obtained. Reports of side effects were few and judged to be of little concern. Piperazine citrate in single dosage is considered an effective public health measure for use in control of roundworm infections.