Nitazoxanide is an important new antiparasitic drug. It is effective for cryptosporidiosis in normal hosts, malnourished children and HIV patients with higher CD4 cell counts. Nitazoxanide is equivalent to metronidazole in giardiasis but may be better tolerated. It has wide spectrum activity against intestinal protozoan and helminth infections. Intestinal protozoa are important but underdiagnosed causes of persistent diarrhea in both developing and developed countries. Empiric therapy with nitazoxanide, which is effective, well-tolerated and modestly priced, may be a reasonable and more cost-effective alternative to pursuing specific diagnoses in selected populations. Copyright © 2005 by Lippincott Williams & Wilkins.