Summary. Paraffin embedded sections of formalin fixed, decalcified, normal, human, vertebral bone were stained immunohistochemically for collagen types I, III and IV using the peroxidase—anti‐peroxidase (PAP) technique. Preparations stained for collagen types I and III were virtually identical in appearance. These substrates were localized to the cytoplasm and fibrillar processes of a population of cells which were sparsely distributed within the haemopoietic compartment of the bone marrow, being particularly prominent in relation to the marrow sinusoids and fat spaces. They would thus appear to parallel the known distribution of reticulum cells, although their morphology differed in some respects from classical descriptions of the latter cell type.

Type IV collagen was found in association with the endothelial lining of the sinusoids. Other connective tissue elements (bone, periosteum, endosteum, blood vessels, etc.) showed characteristic collagen heterogeneity.

These results indicate that collagen is a significant component of the bone marrow connective tissue.