Levels of serum fibrin degradation products were measured by the Staphylococcal clumping test in patients with acute idiopathic anterior uveitis and traumatic anterior uveitis. We found them to be significantly increased (P less than 0.001) in patients with acute idiopathic anterior uveitis (11.0 micrograms/ml). The extent of this increase in the serum levels of fibrin degradation products correlated well with increased severity of the disease. It showed return to normal levels (5.0 micrograms/ml) with the clinical improvement. It increased again with the re-appearance of acute stage of the disease. We found no alteration in the levels of serum fibrin degradation products in patients with traumatic anterior uveitis. We hypothesise that uveal deposition of immune complexes causes secondary platelet damage and intravascular coagulation which results in uveal tissue damage through inflammation.