The effect of intravenous injection of thyrotropin-releasing hormone (TRH) on the plasma concentrations of growth hormone (GH) and growth hormone-releasing hormone (GHRH) was studied in seven patients with acromegaly and in five control subjects. TRH had no effect on plasma GH or GHRH in the five control subjects. A 'paradoxical' increase in plasma GH in response to TRH was observed in four of the seven patients with acromegaly. In these four patients plasma GHRH also increased in response to TRH. No TRH-induced increase in GHRH levels was observed in the other three patients with acromegaly who did not display an increase in GH in response to TRH. The present results imply that GHRH may be involved in the plasma GH response to TRH in patients with acromegaly.