The binding capacity and apparent binding affinity of corticosteroid-binding globulin (CBG) for cortisol was studied in 20 women hospitalized for anorexia nervosa. The binding capacity for cortisol, as determined kinetically at 0 C by the method of Scatchard, was similar in anorectic patients and control subjects, with mean values of 26.9 and 21.9 microgram/100 ml, respectively. The mean apparent affinity constant of CBG for cortisol was found to be significantly (P less than 0.01) lower (14.1 X 10(8) M-1) than that in control subjects (22.3 X 10(8) M-1) and was similar in blood drawn at 0830 and 2000 h. Mean morning total serum cortisol concentrations were higher in anorectic women (23.3 microgram/100 ml) than in controls (10.0 microgram/100 ml; P less than 0.001) and frequently exceeded the binding capacity of CBG. Diurnal variation was present. Mean serum 17 beta-estradiol levels were low (40.0 pg/ml) and serum progesterone was essentially absent, but mean serum testosterone levels were within the normal range. Eight patients who were retested after weight gain, when they were between 76--100% of ideal body weight, exhibited no significant changes in serum steroids or in the binding capacity or apparent affinity of CBG for cortisol.