The efficacy of single-dose ornidazole versus seven days metronidazole in the treatment of giardiasis was tested in a randomized study of 75 Kibbutzim children in Israel. All the children treated were clinically cured, and the parasites disappeared from stool examinations after the first follow-up. By the end of the study (21 days after the beginning of treatment), all the patients remained free of symptoms, but cysts of Giardia lamblia were found in the stools of three children from the ornidazole group (p = 0.24). The possibility of treating Giardia lamblia with ornidazole in a single dose, with results similar to those obtained with a seven-day course of metronidazole, makes this drug a good alternative in the treatment of Giardia lamblia in children, especially if compliance is not assured.