The thyroid status was studied in 19 uremic patients (11 on HD and 8 on CAPD) and in a group of 17 healthy adult patients. In uremic patients T3 and T4 were significantly reduced (p less than 0.001) and rT3 was increased (p less than 0.001). The time course TSH response to TRH showed a lower peak response (in 5 patients it did not exceed 5 microU/ml) which on turn was also delayed (the peak was observed at 60 minutes in 63% of them). TSH concentrations in uremics were increased at 0 time (p less than 0.02), lower at 20 minutes (p less than 0.01) and increased at 120 minutes (p less than 0.02). No difference existed between HD and CAPD. The thyroid response to TSH was normal as showed by a normal percent increase over basal values of T3 concentrations at 120 minutes. Uremic patients also showed a peak GH response at 20 minutes which was not observed in controls. The data exclude the existence on a primary form of hypothyroidism and point to the existence of hypothalamic-pituitary abnormalities, which should not be taken as indicative of secondary and/or tertiary hypothyroidism since FT4 values were normal in HD and increased in patients undergoing CAPD (p less than 0.05) who on turn showed lower plasma albumin concentrations (p less than 0.05).