The activities of acP, alkP, ATP-ase, TPP-ase, non-specific esterase, ASS, AChE and ChE have been investigated by histochemical methods, in the brain of 2 cases of multiple sclerosis. A decrease in the activity of ASS, AChE, ChE and alkP was noticed in the demyelinated white matter of the plaques. Inside the plaques also a loss of ChE activity in the oligodendroglia was observed, whereas the activity of ATP-ase, TPP-ase and acP was increased. The significance of the changes found of the neuroglia hyperactivity in demyelination is discussed.