One hundred sixteen children between 2 and 15 years of age entered a clinical trial of albendazole after examination of their stools revealed ova of one or more intestinal helminths. The drug was administered as a single 400-mg dose (20 ml of 2% suspension) to all the patients except those having Hymenolepis nana infection, who received treatment for three consecutive days. The stools were reexamined on days 7 and 14 posttreatment and after three months for Taenia infections. Patients were considered cured if all parasitological examinations of the feces were negative after treatment. After a single oral dose, albendazole was highly effective in ascariasis (91.9%), ancylostomiasis caused by Ancylostoma duodenale (87.2%), and H nana infection (71.4%). The drug was well tolerated, and no abnormalities were observed in hematological or blood chemistry values. Since the drug is safe and effective as a single-dose treatment of common helminthic infections, it should be considered for mass therapy in the community.