There is increasing evidence that neuroendocrine and temperature responses in humans can be employed to study the functional sensitivity of different 5-HT receptor subtypes. The evidence suggests that the PRL response to LTP is mediated by 5-HT1 receptors, perhaps the 5-HT1A subtype, though further studies are needed to confirm this effect. It is uncertain whether the PRL responses to other 'presynaptic' challenges of 5-HT function, for example, fenfluramine, are mediated by the same post-synaptic 5-HT receptor subtype as that for LTP. Conversely it seems likely that agonists which stimulate 5-HT2/1C receptors increase both plasma PRL and ACTH in humans. There is also evidence that 5-HT1A receptors can increase ACTH secretion. This suggests that in humans as in animals both the 5-HT1A and 5HT2/1C receptors can facilitate ACTH release, though the significance of this dual control is not understood. It is also possible that both 5-HT1A and 5-HT2/1C receptors stimulate PRL release, but 5-HT1A receptors may have a more prominent role in GH secretion. In both human and animal studies 5-HT1A and 5-HT2 receptor agonists may produce opposite effects on body temperature. These recent developments in 5-HT neuroendocrinology have been of great interest, but much is still uncertain. Progress in this field will be considerably advanced by the availability of new selective 5-HT receptor ligands, particularly selective receptor antagonists.