A tissue culture technique which permits the simultaneous measurement of collagen synthesis and bone resportion has been developed. Cultured neonatal mouse calvaria undergo resorption when stimulated by a number of agents including parathyroid hormone, vitamin D, and prostaglandin E 2. Mouse calvaria are of sufficient size to measure the extent of proline incorporation into collagenase-digestible protein. Four chemically diverse stimulators of bone resorption were tested for their effect on collagen synthesis. For each stimulator tested, the dose-response relationships for the stimulation of resorption and the inhibition of collagen synthesis were found to coincide.