OBJECTIVE: To review the pharmacology, pharmacokinetics, adverse effects, drug interactions, dosing recommendations, and clinical efficacy of nitazoxanide, a new antiprotozoal/anthelmintic/antibacterial agent. DATA SOURCES: A MEDLINE search (1966-February 2004) of both human and animal research data published in the English language was conducted. STUDY SELECTION AND DATA EXTRACTION: All primary and review articles pertaining to the MEDLINE search were reviewed for inclusion. Emphasis was placed on randomized, double-blind, placebo-controlled trials. DATA SYNTHESIS: Nitazoxanide is approved for the treatment of giardiasis and cryptosporidiosis (first drug approved for the latter indication) in immune-competent children <12 years of age. Most studies in immune-competent patients have reported clinical and parasitologic response rates close to 80% and 70%, respectively, for both indications. Response rates have been lower in immune-compromised patients. CONCLUSIONS: Nitazoxanide should be available for patients unable to tolerate or adhere to first-line therapy employed for these intestinal protozoa.