I. Introduction AGENERATION ago, in the United States, Rail et al. (1) suggested that the newly discovered cAMP is a second messenger of hormonal action, while in England, Sir Rudolph Peters (2) hypothesized that hormones act through the reorientation of the cytoskeletal (CSK) system. The gap between the two groups of researchers at that time was even greater, since Rall and Sutherland discovered that adrenaline stimulates the generation of cAMP followed by activation of phosphorylase in broken cell preparations (1, 3), while Peters (2) emphasized the whole (intact) cell and not a specific enzyme as the target for hormonal action. The aim of this review is to try to narrow the gap between the ideas of the two schools and demonstrate that the hormonal stimulation of cAMP production and its biochemical actions are controlled by the CSK system. a) Hormone sensitive adenylate cyclase-cAMP system The field of membrane-bound adenylate cyclase (AC) and cyclic nucleotide research had been developing rapidly and is summarized in a few books (3–5), series of international conferences (6) and the Journal of Cyclic Nucleotide Research.