In elderly women with proximal femur fractures, plasma cortisol levels are still elevated 2 weeks after injury. We have now measured the concentrations of adrenocorticotrophin (ACTH) and its precursor peptides (pro-opiomelanocortin plus pro-ACTH) in blood samples obtained in the morning and afternoon from such patients and from old and young control subjects. In healthy subjects, aging had no effect on these variables. Compared with healthy elderly women, the injured women had elevated cortisol but not ACTH concentrations; at both times of day their precursor peptide concentration was increased but probably not enough to affect cortisol secretion substantially. There were no correlations between the concentrations of cortisol, ACTH, and precursor peptides. We have also studied adrenocortical sensitivity after giving dexamethasone overnight. The cortisol responses to graded doses of ACTH did not differ between injured and healthy elderly women, suggesting that their higher cortisol concentrations were the result of stimuli acting independently of ACTH.