Mebendazole, a new broad-spectrum anthelmintic, was used to treat patients with nematode infections--ascariasis, trichuriasis and hookworm. The dosage for adults was 100 mg twice daily for 3 days and for children, 50 mg twice daily for 3 days. Pretreatment and post-treatment egg counts on stool specimens showed that after mebendazole there was a reduction of over 99% in egg count per gram of stool in all three types of infection. The overall cure rates for the infections were as follows: Ascaris lumbricoides, 86.8% (59/68); Trichuris trichiura, 86.0% (37/43); and hookworm, 85.7% (24/28). The drug was equally effective in light and heavy infections. No important side effect was noted with this drug. It is suggested that mebendazole is the drug of choice for trichuriasis and mixed nematode infection.