Furazolidone and quinacrine hydrochloride were compared for efficacy, toxicity, and ease of administration in 45 young children with giardiasis. With the initial course of therapy, the cure rate was 89% (17/19) with furazolidone and with quinacrine it was 64% (9/14) in children less than 5 years and 92% (11/12) in older children. Cure rates for all courses of therapy were 92% (24/26) with furazolidone and 53% (9/17) and 92% (12/13) in the younger and older children, respectively, treated with quinacrine. Quinacrine failure was usually due to severe vomiting. When re-treated with furazolidone, patients were cured. The disadvantages of furazolidone are the large volume of doses and the expense. In this study, furazolidone was more effective and better tolerated than quinacrine for the treatment of giardiasis.