Proteoglycan monomers from articular cartilage of young baboons and of a baboon foetus were submitted to zonal rate centrifugation in sucrose gradients. The peaks obtained were analyzed by gel electrophoresis on polyacrylamide-agarose gels. The proteoglycan monomers corresponding to the bands obtained by gel-electrophoresis of unfractionated proteoglycans were separated in the gradients and the sedimentation distance correlated with the electrophoretic mobility.