The objective was to evaluate whether changes in circulating soluble adhesion molecule levels reflect disease activity in patients with systemic polyarteritis nodosa (PAN). A sandwich ELISA was used to measure soluble (s) intercellular adhesion molecule 1 (sICAM-1), vascular cell adhesion molecule 1 (sVCAM-1), E-selectin, L-selectin and P-selectin in sera and plasma from 22 patients with active PAN, in sera from 13 of these patients taken serially during follow-up, and in sera from 13 healthy controls. At the time of diagnosis, sICAM-1, sVCAM-1 and sE-selectin levels (488.5 +/- 201.3, 1176.5 +/- 514.1 and 60.6 +/- 27 ng/ml, respectively) were significantly higher in patients than in controls (P < 0.0001, P = 0.001 and P = 0.003, respectively). In contrast, sL-selectin levels tended to be lower in patients than in controls. Within the first 7 days after starting treatment, there was a significant increase in sICAM-1 concentrations, which fell thereafter, but did not completely reach normal levels when patients achieved clinical remission. sE-selectin also remained elevated during follow-up. Only sVCAM-1 decreased, tending to reach normal values in inactive disease. Increased levels of sICAM-1, sVCAM-1 and sE-selectin, and decreased levels of sL-selectin, in active PAN suggest immune and endothelial stimulation during disease activity. Abnormal levels of soluble adhesion molecules in clinically inactive patients might reflect persistence of immune activation and/or endothelial cell exposure to a remaining inflammatory microenvironment.