The aim of the study was to observe pulpal collagen synthesis in response to trauma and to glucocorticoid medication. The material consisted of 290 rabbit pulps and 76 human premolar pulps. Collagen synthesis was determined by incubating whole pulps in a medium containing [14C]proline. and measuring the formation of [14C]-hydroxyproline. The effect of glucocorticoids was studiedin vitrousing rabbit pulps. Hydrocortisone and dexamethasone inhibited collagen synthesis, whereas prednisolone had no marked effect. Hydrocortisone was found to inhibit the synthesis of [14C]hydroxyproline in neutral salt soluble and insoluble non-dialyzable collagen fractions. [14C]hydroxyproline in the dialyzable fraction was increased, suggesting that hydrocortisone increased collagen degradation. In the human material, premolar pulps were experimentally exposed and then medicated with capping agents. The contralateral teeth were exposed and capped with other capping materials, in some cases they were left as intact controls. The exposure led to an increase in the collagen synthesis as indicated by increased [14C]hydroxyproline formation and elevated protocollagen proline hydroxylase activity in the pulp. This enzyme activity was suppressed in pulps capped with a glucocorticoid paste. In addition, the collagen synthesis rate was lower in pulps treated with another glucocorticoid containing compound, when compared to pulps capped with a calcium hydroxide preparation.