Albendazole has been tested in an open trial conducted in France, seven countries of West-Africa, Martinique and the People's Republic of China in a total of 1455 patients harboring single or mixed infections caused by round-worms, pinworms, hookworms and whipworms. All patients were closely observed before and after treatment for clinical side effects and hematology and clinical chemistry values were done in about 5% of the cases. Fecal samples obtained before and approximately 15, 16 and 17 days after treatment were examined using the Kato test, and when negative, a concentration technic. In case of ancylostomiasis, a coproculture was carried out for species identification. Following a single oral dose, albendazole was highly effective in enterobiasis (100%), ascariasis (89%), ancylostomiasis caused by Necator americanus (88%) and trichuriasis (70%). The drug did not procedure any significant adverse reactions or modifications of the hematological and clinical blood chemistry values and only 6% of the 1455 patients reported minor side effects.