Tropical sprue is a disease that causes progressive villus atrophy in the small intestine, similar to nontropical (celiac) sprue. The loss of intestinal villi profoundly affects intestinal absorptive function, and patients with tropical or nontropical sprue present with malabsorption. Whereas the etiology of celiac sprue has been elucidated in considerable detail, the etiology of tropical sprue remains obscure. The favored hypothesis is that the disease is either initiated or sustained by a still-undefined infection. Patients with tropical sprue typically present with macrocytic anemia due to malabsorption of folate and/or vitamin B(12). Treatment of tropical sprue with folic acid replacement was introduced more than 50 years ago and has become standard medical treatment. Vitamin B(12) replacement is usually added if there is evidence of B(12) deficiency or malabsorption. Treatment of tropical sprue with folate and B(12) cures the macrocytic anemia and the accompanying glossitis, and often results in increased appetite and weight gain. However, even prolonged treatment with these vitamins fails to restore villus atrophy, and malabsorption usually persists. The benefit of antibiotic treatment of tropical sprue was first documented during World War II, when sulfonamides were used to treat epidemics of tropical sprue in British and Italian troops in India. Antibiotic treatment has since become the standard treatment, and tetracycline has replaced sulfonamides. The recommended length of treatment with tetracycline is 6 months and it is given in combination with folate. The treatment has been shown to normalize mucosal structure in the small intestine and resolve malabsorption in most patients with tropical sprue. However, there is a substantial relapse rate in treated patients who return to, or remain in, endemic areas in the tropics.