Aggressive chemotherapy of leukemia increases the risk of severe infections during treatment-induced myelosuppression. However, the assessment of an infectious origin of neutropenic fever is often difficult. Leukocyte adhesion molecules such as E-selectin, intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) are involved in early inflammatory response. We studied plasma concentrations of their soluble isoforms during 48 treatment courses with myeloablative chemotherapy in 32 leukemic patients. There were 35 febrile episodes during neutropenia. Pneumonia was clinically and microbiologically documented in 15 cases, six had proven infections but normal chest radiograph, and 14 were classified as fever of unknown origin. Longitudinal studies revealed a sustained increase of sICAM-1 plasma levels associated with pneumonia. Increase of sICAM-1 plasma levels distinguished patients with pneumonia from those with fever not related to pneumonia (positive predictive value 0.87, negative predictive value 0.94). Plasma levels of sICAM-1 were elevated in both, fungal and non-fungal pneumonia. Increases of sICAM-1 paralleled first radiographic evidence of pulmonary infiltrations in most cases. In contrast, no elevation of sVCAM-1 or sE-selectin was documented during febrile events prior to recovery of leukocyte counts.