In a patient with suspected Multisclerosis (M.S.), the discovery of a lesion in the anterior optic tracks is of considerable diagnostic importance. If none of the classical clinical signs of optic neuritis can be found, the study of visual evoked responses (VER) and of colour vision is useful evidence for diagnosis. In a population of 102 patients having "possible", "probable" or "confirmed" M.S, we have compared the information provided by both these methods. 27 patients had MS with a known optic neuritis: the VER and colour vision of all of them was altered, either unilaterally or bilaterally. 75 patients had "possible" or "probable" MS without a history of optic neuritis. For 34,7%, the discovery of a dyschromatopsia showed a lesion in the optic nerve. In 68%, only the increased latency in VER demonstrated an optic neuritis. It should be noted that for all the patients with "probable" or "confirmed" MS, the VER latency was increased. The study of colour vision is therefore in our opinion, an excellent way of investigating anterior optic tracks lesions. When the study of colour vision is not sufficient, the recording of VER is a reliable technique and a very valuable acquisition in neuro-ophthalmology.