To characterize and compare the expression of PECAM-1 in unstimulated and tumor necrosis factor α(TNF-α)-stimulated tissues of mice. Binding and non-binding monoclonal antibodies (mAb) were radio-labeled and injected into wild-type mice deficient of P-selectin, CD18, or ICAM-1. The relative accumulation of binding mAb (PECAM-1 mAb) was determined in wild-type mice following a 25 µg/kg i.p. injection of TNF-α and in mutant mice under basal conditions. Under unstimulated conditions, PECAM-1 was significantly expressed in all tissues examined, with no changes occurring after TNF-α stimulation. An equivalence of PECAM-1 expression was observed in unstimulated tissues among wild-type mice and mice that are genetically deficient in either CD18, ICAM-1, or P-selectin. The level of PECAM-1 expression in different vascular beds was highly correlated to published values of endothelial surface area. Normalization of previously published values of ICAM-1, VCAM-1, E- and P-selectin expression relative to PECAM-1 expression in the same tissues revealed a diminished organ-to-organ variability in expression of the different adhesion molecules. Estimates of adhesion molecule expression in lung and brain were most profoundly affected by normalization to PECAM-1 expression. These findings support the use of PECAM-1 expression in regional vascular beds as an indicator of endothelial cell surface area.