PRL secretion was evaluated in 14 males with chronic renal failure on long term hemodialysis. Twelve had basal hyperprolactinemia. Ten subjects were challenged with TRH in doses ranging from 200-1000 μg. None of them responded to 200 or 500 μg TRH, although 2 of 4 subjects tested did respond to 1000 μg TRH. In contrast, all 4 subjects challenged with metoclopramide did have PRL responses which were indistinguishable from those of the controls. These results indicate that there is a dissociation in responsiveness to metoclopramide and TRH in chronic renal failure.