The somatotropic, thyrotropic and corticotropic functions were investigated in 8 patients with idiopathic pituitary dwarfism. Particularly interesting were the results obtained from studies of the thyrotropic function. In the absence of clinical and conventional laboratory indices of hypothyroidism, measurement of plasma immunoreactive T3 and TSH before and after iv administration of 400 μg of TRH suggested the presence of borderline hypothyroidism. Basal plasma T3 values ranged from 20 to 55 ng/100 ml with a mean of 36.2 vs 55–160 ng/100 ml with a mean of 107. Moreover, plasma T3 response to TRH, although present, was markedly lower than in the controls (20–90 ng/100 ml with a mean of 62 vs 100–175 ng/100 ml with amean of 127). Plasma TSH response to TRH appeared markedly delayed and prolonged (maximal rise at 60 min instead of at 20 min). Also of interest were the results obtained from studies of the corticotropic function. The maximal plasma ACTH values after insulin-induced hypoglycemia was 91 + 17.5 pg/ml in our patients vs 460 + 58 pg/ml in the controls. Also, plasma corticosteroid responses to provocative tests were lower than in the controls. However, only in thecase of plasma ACTH responses was the difference significant, suggesting an impairment of corticotropic function. The present study demonstrates that in our patient group, besides the somatotropic function, impairment also involves the thyrotropic and corticotropic functions. In addition, our study outlinesthe diagnostic value of basal plasma T3 and of plasma T3 and TSH responses to TRH in detecting borderline hypothyroidism, and that of plasma ACTH responses to provocative tests in detecting impairment of the corticotropic function.