The influence of ageing upon the urinary steroids, the correlation between the excretion of creatinine and the urinary steroids and between the renal clearance of creatinine and urinary steroids were studied in healthy men of different ages. The results show the well established decrease in the urinary excretion of steroids that occurs with ageing. The correlation coefficients demonstrate a good linear correlation with renal clearance of endogenous creatinine, but a poor one with the excretion of creatinine. The response to ACTH is lower in the older group as judged by the urinary 17-keto-steroids and 17,21-dihydroxy-20-keto-steroids. © 1963 Holden-Day, Inc.