The serum alpha-1 antitrypsin level was measured in 60 patients with endogenous uveitis, 27 patients with phacoallergic endophthalmitis, 12 patients with phacolytic glaucoma, and 58 healthy subjects. Thirty-four patients with endogenous uveitis were also followed up for 6 months after treatment, and the serum alpha-1 antitrypsin level was measured again. There was a significant rise in the serum alpha-1 antitrypsin level in cases of endogenous uveitis and phacoallergic endophthalmitis but no alteration in cases of phacolytic glaucoma. Among the patients with endogenous uveitis the level was significantly raised in cases of anterior uveitis, but there was no change in cases of posterior uveitis. A significant rise was seen only in cases of acute anterior uveitis but not in chronic anterior uveitis. The serum alpha-1 antitrypsin level was unaltered in endogenous uveitis despite clinical improvement.