The proteoglycans (PGs) are a large and varied family of complex macromolecules whose physical properties are dominated by their large sulfated polysaccharide chains (for a recent review, see ref. 1 ). They are widely distributed in the animal kingdom, but are not associated with any particular anatomical or cellular sites, being instead almost ubiquitously present both on cells and within extracellular matrices. On cells they are usually constituents of the plasma membranes, though in the case of various cells of the hemopoietic lineage they can also be found in high concentrations within secretory granules.