Plasma catecholamines assayed by a double isotope radio enzymatic method were studied in the basal state and during a thyrotrophin-releasing hormone (TRH)-test in 7 acromegalics, divided into 2 groups: active and non-active acromegalics, according to clinical and biological criteria. Basal plasma norepinephrine levels were significantly increased in the active group 648 +/- 22 pg/ml (P less than 0.001) and were in the normal range in the non-active group 439 +/- 26 pg/ml. Basal plasma epinephrine values were not significantly different in the 2 groups 59 +/- 15 pg/ml vs 34 +/- 7 pg/ml. During a TRH-test, norepinephrine levels remained elevated (P less than 0.001) in the active group, and the difference between the 2 groups was enhanced during the test. On the other hand the 2 patients who responded to TRH demonstrated an increase of norepinephrine levels. Our results suggest that TRH may stimulate norepinephrine release in acromegalics with an active response to TRH.