In many acromegalic patients the paradoxical release of GH in response to TRH has been well documented, but the mechanisms underlying this phenomenon are not understood. It has been suggested that aberrant GH secretion may result from TRH endogenously synthesized by the adenoma. In 32 adenomas from acromegalic patients, TRH-like immunoreactivity (TRH-LI) was measured using 2 well characterized antisera. TRH-LI was not detectable in 10 samples, and in 19 samples, TRH-LI was measured only by the less specific antibody. With the TRH-specific antibody, TRH-LI was identified only in 3 samples, 2 of which contained exceedingly high concentrations (40 and 96 pg/mg tissue). In the latter 2 samples, prepro-TRH messenger ribonucleic acid was identified by Northern blot analysis, but not in the control tissue sample of a patient without pituitary disease and also not in the other adenomas analyzed by this technique. Transcripts of the TRH receptor were almost undetectable in all adenomas analyzed. For the TRH-degrading ectoenzyme, a potential regulator of TRH signals at adenohypophyseal target sites, transcripts were significantly expressed only in the TRH-producing adenomas. We conclude that the TRH-signaling elements examined are, in general, not directly involved in the mechanisms causing paradoxical GH secretion in acromegalic patients.