Tibiae of 12-day embryonic chickens were grown in organ culture in synthetic medium for 48 h in the presence of various levels of hyaluronidase. This treatment: (1) removed between 49 and 86% of hexosamine-containing material from the rudiments, and the level of hydroxyproline remained just below that in controls; (2) reduced the length and weight of the rudiments; (3) increased the total protein and DNA content in bone but reduced the amount gained in cartilage; (4) altered the fine-structure of the epiphysial chondroblasts; (5) failed to affect the rate of incorporation of isotopic uridine and leucine. When explants were subcultured in normal medium for a further 5-day period, the degree of recovery was dose-dependent; the final level of constituents in bone and cartilage of some rudiments exceeded those in controls. Hyaluronidase greatly enhanced the synthesis of hexosamine-containing materials during the period of treatment of the rudiments and a second, but generally smaller, wave of excess synthesis occurred during the recovery phase; initially, large amounts of polymer chains were released into the medium, but they were incorporated into the tissues rapidly towards the end of culture. Characterization of the glycosaminoglycans indicated, also, that an abnormal type of polymer chain was synthesized and rejected by the tissue. The rate of synthesis of both hydroxyproline, and hence collagen, and non-collageneous protein was also enhanced during the recovery period. The results showed that the cells could re-establish their normal environment following the initial loss of intercellular macromolecules, and that such changes in the concentration of constituents enhanced the synthetic responses of the cells.