• Corneal fibroblasts were studied to determine if they have the ability to synthesize and secrete complement components in tissue culture. Culture media were assayed for functional complement activity of C1, C4, C2, C3, C5, C6, and C7 with the use of 50% hemolysis of sensitized sheep RBCs. Only C1 showed a progressive increase in hemolytic activity at days 3, 5, 7, 9, and 11 of tissue culture. This increase in hemolytic C1 could be reversibly inhibited by cycloheximide, an inhibitor of protein synthesis. Corneal fibroblasts may be a potential source of C1 in the cornea.