Children with thermal injuries have an unusually high incidence of hypertension during the course of their postinjury care. This study investigates the activity of the renin angiotensin system during the postinjury period. Sustained hypertension occurred in three of 11 children studied. All three cases demonstrated markedly elevated plasma renin levels (>2IRU x 104). Two of five children with episodes of hypertension also demonstrated abnormally high plasma renin. No normotensive patients had markedly elevated renin levels. The mechanism directing elevated renin secretion may be related to changes in regional blood flow in addition to the stimulus of increased catecholamine activity. A markedly elevated plasma renin may be predictive of the development of hypertension.