To study the etiology of chronic childhood diarrhea among Nigerian children, 142 patients, aged 6 months to 5 years, with diarrhea for at least 1 month, were evaluated; the study took place during January-December 1983 at the Ahmadu Bello University Teaching Hospital, Zaria, Northern Nigeria. Enteropathogenic agents were identified in stools of 90 (63%) patients. Giardia lamblia and Entamoeba histolytica were most commonly detected, representing 41% and 23%, respectively, of all parasitic pathogens. In children with negative stool microscopy, chronic diarrhea was associated with primary lactose intolerance (2 cases), abdominal tuberculosis (2 cases), hyponatremia, low serum albumin, anemia due to sickle cell disease, or Staphylococcus aureus infection. In contrast with chronic diarrhea etiologies reported among children in Europe and North America, infections were the major cause of chronic childhood diarrhea among these children. In general, it is accepted that intestinal infection usually produces acute diarrhea--and that, if the host fails to mount a competent immune response, if there is repeated exposure to infectious agents, or if severe infection damages a substantial proportion of absorptive cells, then severe, protracted diarrhea may result. The high case fatality rate of 9% in this series was associated with specific infectious complications of septicemia, bronchopneumonia, lobar pneumonia and measles. Severe malnutrition also worsened the prognosis in chronic diarrhea. The results indicate that early detection and treatment of amebiasis and giardiasis is a useful approach in the treatment of chronic diarrhea cases among children.