Mononuclear leukocyte (MNL) beta 2-adrenergic receptors and their coupled adenylate cyclase system were studied in underweight anorectics (n = 12), weight-recovered anorectics (n = 8), bulimics (n = 8), and age- and sex-matched controls (n = 39). Compared with controls, underweight anorectics had significantly fewer MNL beta 2-adrenergic receptor sites (Bmax) but did not differ in binding affinity (Kd). Weight-recovered anorectics and bulimics did not differ from controls on either Bmax or Kd. Compared with controls, all three patient groups had significantly reduced plasma levels of triiodothyronine (T3), while only underweight anorectics had significantly elevated plasma levels of cortisol. Plasma norepinephrine (NE) response to orthostasis was significantly lower in the three patient groups than in controls. The reduction in beta 2-adrenergic receptor number in underweight anorectics could reflect their elevated cortisol and reduced T3 levels. The decrease in beta 2-adrenergic receptor sites, together with the lower NE response to orthostasis, could be responsible for the reduced sympathetic activity of underweight anorectics.