- Proline-(14)C was administered to five adult rhesus monkeys, and the degradation of collagen was followed by the excretion of hydroxyproline-(14)C. The results suggested the presence of at least three separate pools of collagen with half-lives of 1 to 2, 2 to 3, and 50 to 70 days. The monkeys were killed after 44 days; at that time the specific activity of the hydroxyproline-(14)C in urine was found to be four to five times that of the hydroxyproline in soluble collagen and 81 to 93% that of hydroxyproline in insoluble collagen. The relationships between urinary hydroxyproline and the degradation of collagen were similar to those previously demonstrated in rats. Parathyroid hormone was administered daily to two of the monkeys from the 27th to the 44th day of the study. The parathyroid hormone increased the amount of hydroxyproline-(14)C excreted, but there was no significant change in the specific activity of the urinary hydroxyproline-(14)C. Since under the conditions of the experiment insoluble collagen was the only possible source of hydroxyproline-(14)C of relatively high specific activity, the results indicated that parathyroid hormone directly or indirectly increased the degradation of insoluble collagen. The results also suggested that parathyroid hormone increased the degradation of soluble collagen, but the relative magnitude of this effect was not clearly established.