IT has been suggested that reduction of internodal length may be a feature of remyelinated central nerve fibres as it is of peripheral nerve fibres1. As the technique for measuring internodal length of nerve fibres in the central nervous system (CNS) is tedious and requires a high degree of skill and patience from the investigator2, it is unlikely that this method can be applied to routine neuropathological investigations. Recent ultrastructural studies on remyelination in the mouse, following primary demyelination induced by feeding cuprizone (Bis - cyclohexanone - oxaldihyrozone)3–5 have shown that measurements of the relationship between myelin sheath thickness and axon diameter provides an easier method of identifying remyelinated axons.