OBJECTIVES: To describe the pattern of expression of intercellular adhesion molecule-1 (ICAM-1) at the surface of human osteoblasts (Ob) recovered from normal (control), osteoporotic (OP), and osteoarthritic (OA) bone. To relate ICAM-1 expression in OA Ob with interleukin-6 (IL-6) and prostaglandin E2 (PGE2) production. MATERIALS AND METHODS: Trabecular bone specimens were taken from patients suffering from OA of the hip (n = 19) or knee (n = 19) or from hip fracture caused by osteoporosis (n = 10). Control bone specimens came from the posterosuperior iliac crest (n = 5) and from the femoral condyle of organ donors (n = 6). Bone explants were digested with collagenase and cultured. Ob were obtained after 6 weeks. ICAM-1 expression was studied by immunocytology. IL-6 and PGE2 were evaluated by standard ELISA. RESULTS: Average ICAM-1 expression was different between control and OP bone (P < 0.02). Separation of specimens into high and low ICAM-1 expression showed a significant difference between high and low ICAM-1 expressors. The distribution of specimens after subclassification into high or low ICAM-1 expression groups revealed only 18.2% of patients in the high expression group for the controls, compared to 70% for OP bone (P < 0.03), 52.6% for hip OA and 47.4% for knee OA. IL-6 and PGE2 levels in OA Ob from both groups were found to be significantly elevated with high ICAM-1 expression compared to low ICAM-1 expression. CONCLUSION: The results show that ICAM-1 expression in human bone seems to be pathology-dependent and correlates with IL-6 and PGE2 production, at least in OA individuals. This implies that ICAM-1 could discriminate functionally different populations of Ob and possibly alter the clinical evolution of the disease.