A new anthelmintic drug, albendazole, has been tested in a multicenter double-blind placebo controlled study in 392 patients from France and West Africa in children and adults with single or mixed infections caused by roundworms, hookworms, whipworms, threadworms and tapeworms. All patients were closely observed before and after treatment for clinical side effects, hematological or clinical blood chemical changes. Fecal samples obtained before, and 7 days and 21 days after treatment were examined using a concentration technic (Ritchie), a coproculture (Harada-Mori) and an egg count (Kato). Following a single dose of 400 mg in adults, cure rates of 96% in ascaridiasis, 96% in ancylostomiasis caused by dose of 400 mg in adults, cure rates of 96% in ascaridiasis, 96% in ancylostomiasis caused by Ancylostoma duodenale, 90% in ancylostomiasis caused by Necator americanus and 76% in trichuriasis were recorded. About 48% of the patients infected by Strongyloides stercoralis were cured following administration of 400 mg per day for 3 consecutive days. The efficacy of half of the adult dose (200 mg) was much lower in children. None of the patients who received placebo were cured. The drug did not produce any significant side effects and approximately the same numbers were reported in the albendazole and the placebo groups. No variations of the hematology and clinical blood chemistry values were recorded.