Soluble interleukin-2 receptor (sIL-2R) levels were measured in the serum of 27 patients with retinal vasculitis, 16 with vasculitis purely isolated to the eye (RV) and 11 with vasculitis associated with a systemic inflammatory disease (RV+SID). Levels of sIL-2R were statistically significantly increased (μ986, SD 845 U/ml, p = 0.013) only in the RV+SID group as compared to healthy controls. The highest levels being found in patients with sarcoidosis (μ1436, SD 1083 U/ml). There was no correlation with disease activity or with systemic corticosteroid therapy. Serum sIL-2R measurements appear to be of limited use in the management of patients with retinal vasculitis, but may be of value in those patients with sarcoidosis. Longitudinal measurements with larger numbers of patients are required to confirm this. Serum sIL-2R levels were also statistically significantly increased (μ843, SD 171 U/ml, p<0.0001) in 21 patients with Fuchs' heterochromic cyclitis. As this is a chronic condition with mild inflammatory activity and no associated systemic disease, the explanation for this finding is unknown.