Serum levels of TSH and GH were measured by radioimmunoassay after iv injection of 500 mug of TRH in 9 undialysed patients and 12 dialysed patients with chronic renal failure and in 6 healthy subjects. The basal level of the serum TSH was significantly higher in patients with chronic renal failure than that in healthy subjects. In healthy subjects, serum TSH rose to a maximum level 30 min after TRH injection, while in patients with chronic renal failure, serum TSH rose to a maximum level 60 min after TRH injection. The mean maximum increment of serum TSH in healthy subjects was significantly higher than that in patients with chronic renal failure. Although TSH levels rapidly decreased after initial rise at 30 min after TRH administration in healthy subjects, these did not show significant changes at 60 and 120 min compared with values at 30 min after TRH administration in both dialysed and undialysed patients. The basal level of serum GH was significantly higher in dialysed patients with chronic renal failure than in healthy subjects. Serum GH level was much higher in dialysed patients at 30 min after TRH INJECTION COMPARED WITH THAT IN HEALTHY SUBJECTS. These findings may indicate that the response of the pituitary to TRH is abnormal and that the turnover of TSH and GH is decreased in patients with chronic renal failure.