Hyaluronate turnover is correlated with morphogenetic events during chondrogenesis in the regenerating newt limb and in the chick embryo limb and axial preskeleton and during development of the chick embryo cornea. In vitro hyaluronate, in concentrations as low as 1 ng/ml, blocks the formation of cartilage—like aggregates in high density stationary cultures of stage 26 chick embryo somite cells. This inhibition is prevented by hormones known to promote skeletal development and by adenosine 3',5'cyclic monophosphate. An hypothesis is discussed in which (1) hyaluronate may interfere with cell interactions leading to aggregation, encapsulation by matrix and consequent immobilization and (2) hyaluronate turnover could provide a means of timing of morphogenetic events such as cell migrations, allowing sufficient accumulation of cells prior to overt differentiated tissue formation.