During a 24-month period 446 children with diarrhea and 16 controls had examination of their stools for leukocytes and for occult blood. Fecal leukocytes were found in 36, 16 and 18% of children with Salmonella-Shigella-Campylobacter, rotavirus or enterotoxigenic Escherichia coli, or cryptosporidial diarrhea, respectively. Similarly 43, 39 and 38% of these groups, respectively, as well as 13% of controls had occult blood. Notably 70% of 10 Shigella cases had fecal leukocytes. In 166 children with mixed pathogens leukocytes were seen in 27 and 8% of children with Salmonella-Shigella-Campylobacter or noninvasive pathogen, respectively. Likewise 44 and 18% of these groups had occult blood. Agreement between both tests being positive was poor, the highest result being 50% for Shigella. Dysentery combined with both tests positive was associated with 15 (88%) cases of invasive agents present in stool cultures, and combination of dysentery with fecal leukocytes was associated with 21 (72%) cases of invasive agents recovered. The results of these tests should be interpreted in the context of the clinical situation. A combined clinical-epidemiologic and screening tests-based approach to infectious diarrhea of childhood is suggested.