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The intercellular substance of the pulp of fully erupted, healthy, human permanent premolar teeth was studied by light microscopy. Histological and histochemical methods were applied to sections from whole, decalcified teeth and isolated, undecalcified pulps, fixed with phosphate-buffered formalin and embedded in paraplast. Fibres were mainly collagen; they formed a meshwork progressively more dense from the crown to the root apex; in the crown the fibre meshwork was denser at the periphery than in the center of the pulp. Coarse bundles of collagen fibres were found in the apical part of the pulp of about one every third teeth. Glycoproteins, recognized thanks to their P.A.S. positivity, were abundant in the basal membranes of vessels and nerve fibres and between odontoblasts, but scarce in the remaining pulp tissue. Glycosaminoglycans, recognized thanks to their alcianophilia, were more abundant in the vessel wall and in the areas with coarse bundles of collagen fibres than elsewhere in the pulp; also, they were more abundant at the periphery than in the center of the pulp. As judged by staining with alcian blue at critical electrolyte concentration, glycosaminoglycans were mostly hyaluronate, with low amounts of condroitinsulphate and dermatansulphate; some heparansulphate or keratansulphate was present only in the regions with coarse bundles of collagen fibres. The morphological and histochemical differences found among different regions of each pulp and among different pulps as well provide a basis to recognize and interpret inter-regional and inter-individual variations in the pulp response to physiological and pathological modifications affecting the hard tissues of the teeth.