Studies on polypeptide receptors a critical view on the mechanism of ACTH action. 
Recent work on ACTH receptors in adrenal cells and adipocytes is reviewed.  It is suggested that ACTH acts on two types of receptor: an adenylate cyclase receptor and another one that helps to guide cAMP into the correct compartment.  The introduction of the term holoreceptor to indicate a unit that is recognized by the hormone and is able to produce a measurable effect, and of the terms discriminator, transmitter and effector to indicate the functional subunits of the holoreceptor is suggested as a measure enhancing clarity and flexibility of communication in this very complex field.