ObjectiveIn a recent study, we found high levels of erythropoietin (EPO) in patients with diabetic macular oedema (DME), suggesting a role of EPO in the pathogenesis of this condition. To investigate a possible relationship between EPO and other diseases causing macular oedema, we determined vitreous levels of this peptide in patients with macular oedema secondary to retinal vein occlusion (RVO) and compared them with levels in patients with DME and control patients. Vitreous and serum samples were obtained from patients with macular oedema secondary to RVO, DME, epiretinal membrane, and macular hole (controls). EPO was measured by radioimmunoassay. No differences were found in median vitreous EPO levels between patients with RVO and controls: RVO, 76 mU/ml (30-806) vs controls, 25 mU/ml (10-75) (P0.105). Median EPO concentration was higher in DME patients than in patients with RVO or controls: DME, 430 mU/ml (41-3000) vs RVO, 76 mU/ml (30-806) (P0.0001) vs controls, 25 mU/ml (10-75) (P0.0001). EPO levels are not elevated in patients with macular oedema secondary to RVO. Patients with DME have high levels of EPO. These results suggest that EPO could be involved in the pathogenesis of diabetic retinopathy, but not in macular oedema secondary to RVO. © 2009 Macmillan Publishers Limited All rights reserved.