One hundred children were entered into a randomized study to compare the efficacy and safety of furazolidone and metronidazole when given in liquid suspension for treatment of giardiasis. The study was conducted between May 1985 and February 1986. Dosages were calculated on the basis of body weight, and treatment lasted 10 days. Clinical diagnosis of giardiasis was confirmed by the presence of Giardia cysts in stools. Children were excluded from the study if stool culture was positive for pathogenic bacteria. Eighteen of the 100 children were withdrawn from the study because of noncompliance with the protocol. Of the 82 remaining patients, 37 received furazolidone and 45 metronidazole. No statistically significant differences in efficacy between treatments were found. With the exception of one case of urticaria, which occurred in a patient who received metronidazole, both drugs were well tolerated. In this study, furazolidone and metronidazole were equally safe and effective in treating children with giardiasis.