The AA. have studied the effect of the bovine GH on the cellular and intercellular components of the chick embryo tibias cultured organotypically. They have observed a strong increase of the proliferative activity of the chondroblasts such as showed by a stronger uptake of the tritiated timidine by traited tibias in comparison with the control tibias. The chondroblasts of the traited tibias show an increase of some enzymatic activities connected with the aerobic cycle and of the UDPG-DH, connected with the uronic acids cycle. In the amorphous matrix of the traited tibias they have showed a greater polimerisation and sulfation of the condroitinesulfate A and C, which, almost exclusively, constitute the mucopolisaccharidic component of the matrix.