PURPOSE. To evaluate the degree of phosphorylation of vitreous proteins in patients with type 2 diabetes mellitus and diabetic retinopathy compared with a group of control subjects without diabetes and of similar age and sex. METHODS. In samples obtained after vitrectomy for diabetic retinopathy in patients and for macular hole in control subjects, immunoblot techniques were applied to a mini-array system for quantification of a wide range of chemokines and vasoactive peptides and proteins. Antiphosphotyrosine antibody was used for tyrosine phosphorylation evaluation and results were expressed as the percentage of variation compared with that in control subjects. RESULTS. Samples from eight patients with type 2 diabetes and from eight control subjects were analyzed. The total quantity of proteins analyzed was similar in both patients and control subjects. Tyrosine phosphorylation was very significantly decreased (<20%, P < 0.05) in diabetic patients with respect to the control group in growth-related oncogene, human cytokine I-309, interleukin-13, monocyte colony-stimulating factor, macrophage-derived chemokine, stem cell factor, transforming growth factor-β1, angiogenin, and oncostatin M. A significant decrease in phosphorylation (between 20% and 40%, P < 0.05) was observed in epithelial neutrophil-activating peptide 78; granulocyte colony-stimulating factor; granulocyte-monocyte-stimulating colony factor; IL-5, -6, -7, -8, -10, and -12p40p70; monokine induced by interferon-γ; macrophage inflammatory protein 1-γ; and normal T expressed and secreted cytokine (RANTES) in comparison with that in the control subjects. The greatest decrease in phosphorylation status was found in IL-1-α and -1β. CONCLUSIONS. Diabetic retinopathy is associated with a decrease in tyrosine phosphorylation of many vitreous proteins which may indicate an alteration in protein functionality or action even before significant quantitative variations. Copyright © Association for Research in Vision and Ophthalmology.