Seventeen patients with retinal vasculitis, eleven with the peripheral type (Eales' disease) and six with the central type, were investigated to detect the presence of circulating immune complexes (IC) which might then be related to the pathogenesis of their disease. A systemic disease process was identified in six. IC in serum were inferred by the presence of complement (C) activation, rheumatoid factor, Clq or monoclonal rheumatoid factor precipitins, anticomplementary activity, elevated cryoglobulins, inhibition of erythrocyte-antibody (IgG-EA) rosette formation, increased numbers of peripheral blood lymphocytes bearing surface Ig, and spontaneous neutrophil chemotatic activity in plasma. Two or more parameters were positive in thirteen of seventeen patients, with chemotactic activity (69%) and inhibition of EA-rosette formation (59%) being the most frequently positive tests. No immunological differences were detected between the peripheral and central retinal-vasculitis groups. Several IC systems may operate in a give patient.