Glucocorticoids have been shown by others to increase the synthesis of elastin both in aortic tissue of embryo chicks and in cells derived from fetal ligamentum nuchae. This report describes the effects of hydrocortisone on the production of elastin in aortic tissue of developing chick embryos and chicks. While the effect of hydrocortisone on elastin synthesis is stimulatory in the 14 day chick embryo and the day-old chick, the same dose of this glucocorticoid has no effect on elastin production in the 7 day old chick and significantly inhibits synthesis of elastin in the 14 day old chick. These age-related alterations in elastin production in response to hydrocortisone cannot be attributed to an effect of the steroid on the pool size of the radioactively labelled amino acid used to measure elastin synthesis.