Among 10 children with giardiasis, eight had iron deficiency; iron deficiency anemia was the main complaint in three. Evaluation of iron absorption by the oral iron load test demonstrated a subnormal response (i.e., increase in serum iron levels of less than 100 micrograms/dl) in all eight patients with iron deficiency. In contrast, in two iron-sufficient patients with giardiasis the response to an oral iron load was normal. Xylose absorption was abnormal in five of the 10 patients. After metronidazole dosing, iron absorption became normal in seven patients but remained abnormal in one patient, who also had IgA deficiency. Xylose absorption became normal in all five patients who underwent a second test, but remained abnormal in the patient with IgA deficiency. Concomitant morphologic-studies of jejunal biopsy material from these patients revealed moderate changes in the intestinal mucosa of two patients. We conclude that malabsorption of iron is a complication of giardiasis.