Technetium Tc 99m-labeled hexamethylpropyleneamine-oxime (Tc-HMPAO) scintigraphy has been evaluated in adults with inflammatory bowel diseases and has shown promising ability to define intensity and extent of disease. To evaluate the method's utility in children, we studied 27 pediatric patients-23 with inflammatory bowel diseases and 4 control subjects without abdominal inflammation. Autologous leukocytes labeled with Tc-HMPAO were reinjected into each patient and serial scans were obtained up to 4 hours later. None of the control subjects had any uptake of Tc-HMPAO by the bowel. Disease localization as defined by the scan correlated well with that visualized in surgical specimens from five patients, at endoscopy in three patients, with barium studies of two patients, and with computed tomography scanning of the abdomen in one patient. A "scan score" was calculated by comparing uptake of tracer in five bowel segments with iliac crest bone marrow activity. Scan score correlated much better with clinical disease activity (correlation coefficient = 0.62) than did the erythrocyte sedimentation rate (correlation coefficient = 0.24). Scintigraphy with Tc-HMPAO appears to be useful in evaluation of disease localization and intensity in children with inflammatory bowel disease.