This report describes and illustrates the results of the histopathological and histochemical investigation on five slow-growing tumors of the central nervous system: four meningiomas and an ependymoma of the spinal cord. We have studied, by means of polarizing microscopy, sections stained with picro-sirius red F3BA that enhance the birefringence of collagen and reticulum fibres. The heterogeneous behaviour of the distribution of the collagen let us conclude that the fibrillar component of the extracellular matrix have a scarce importance for the speed of growth of these tumours.