EPO and optic neuritis: In this study, we used clinical and magnetic resonance imaging (MRI) data obtained during the erythropoietin treatment trial [1] in order to investigate (i) the influence of erythropoietin on conversion of clinically isolated optic neuritis into MS and (ii) its effects on cerebral lesion load and the numbers of gadolinium-enhancing lesions during the 16 weeks following treatment.