sICAM-1 has been elevated in sera of specific inflammatory diseases, and circulating sICAM-1 concentrations reflect disease activity in these diseases. We measured circulating sICAM-1 concentrations and serum angiotensin-converting enzyme (SACE) activity in patients with sarcoidosis. Patients with sarcoidosis had significantly increased circulating sICAM-1 concentrations (62.8 +/- 33.5 U/ml) and SACE activity (23.7 +/- 7.4 U/l) compared with controls (circulating sICAM-1 50.9 +/- 12.1 U/ml, and SACE 13.5 +/- 3.8 U/l). Successive measurements showed that circulating sICAM-1 values changed in parallel with disease activity in sarcoidosis. In the progressive disease group (progressed or without change for 2 years or more), circulating sICAM-1 values (102.2 +/- 35.3 U/ml) at the time of diagnosis were significantly increased compared with those in the regressive disease group (disappeared or regressed within 2 years) 46.4 +/- 12.6 U/ml). However, there was no significant difference in SACE activity of the regressive and progressive disease groups. Fifteen patients with a high value of circulating sICAM-1 (> 75 U/ml, mean of controls + 2 s.d.) all had progressive disease, while only 15 of 44 patients with a high value of SACE had progressive disease. Circulating sICAM-1 will be a useful blood marker to predict outcome and to monitor disease activity in sarcoidosis.