To evaluate GH pituitary responsivity to nonphysiological stimuli in insulin-dependent (type I) diabetes, a TRH test (200-micrograms iv bolus) was carried out in 31 type I diabetics (16 females and 15 males). TRH was capable of inducing GH responses in most of the studied patients, with a striking difference between the sexes; responses were documented in 7 of 15 males and in 13 of 16 females. Linear regression analyses of the results showed a positive correlation between basal values and peak levels of GH and a negative correlation between GH peaks and the ages of the patients. No correlation was found between GH values (basal and peak levels) and blood glucose levels or duration of disease. In conclusion, our results support the observation that GH secretion in diabetes is abnormal. TRH induces GH secretory responses, especially when GH basal values are elevated and in female patients. Pituitary GH responsiveness to TRH shows a progressive decline with advancing age unrelated to the duration of the disease or the presence of retinopathy.