Hyaluronic acid and collagen gel produced a mild inflammatory reaction in normal monkey eyes. Vitreous uptake of iodine I 131 labeled protein, however, remained abnormal for several months after other evidence of inflammation had resolved. Scleral diathermy or cryoapplication increased vitreous isotope uptake five to eight times in the absence of clinical signs of inflammation. The same vitreous substitutes in eyes with markedly abnormal vascular permeability produced a more severe inflammatory reaction at two days. Intensive corticosteroid therapy partly ameliorated this increased reaction.