This report describes an investigation of the effects of developing hypertension on the synthesis and accumulation of insoluble elastin in the thoracic aorta of young rats. Uninephrectomized male rats were made hypertensive by administration of deoxycorticosterone acetate and addition of 1% NaCl to their drinking water. Divergence of systolic blood pressures between treated and control animals and hypertrophy of the vessel began after about 2 weeks of treatment. Coincident with the appearance of hypertrophy, there was an increased accumulation of insoluble elastin in the aorta and a large increase in the capacity of the aortic tissue to synthesize elastin. However, in spite of continued increases in blood pressure and vessel hypertrophy, this effect on elastin synthesis and accumulation was transient. The results of this study suggest that synthesis of elastin in aortic tissue of young rats is highly sensitive to alterations in blood pressure.