Pyrantel pamoate was administered orally as a single dose in a suspension or chewable tablet to 379 patients with helminth infections. Single doses of oral suspension were administered for 3 consecutive days to 89 patients. A modified Stoll technique and Richie's concentration method were performed twice before treatment and at 10 and 30 days after treatment. In a single dose of about 5 mg per pound of body weight (base activity) the cure rate for ascariasis was 96.7%; the reduction of the egg count in one case not completely cured was 98%. Significant activity was also observed against Necator americanus; however, at the dosages employed, it was not superior to other agents currently in use. No significant activity was noted against Trichuris trichiura. Clinical observation showed that both formulations were well tolerated by the patients. No significant changes attributable to therapy were observed in determinations of hematopoetic, liver, or renal function.