Actions of thyrotrophin‐releasing hormone (TRH) have generally been confined to the central nervous system (CNS). We have studied the effect of increasing doses of TRH i.v. (8, 40, 200 and 1000 μg/h) on pentagastrin‐stimulated gastric secretion in ten normal individuals. All doses caused stepwise inhibition of gastric juice (volume), acid and pepsin output. When employing the largest dose of i.v. TRH (1000 μg/h) the inhibition was 44% for gastric volume, 51% for acid output and 57% for pepsin output. This study shows that TRH inhibits gastric secretion, and indicates that TRH has actions outside the CNS in man. Copyright © 1979, Wiley Blackwell. All rights reserved