Recent years have seen tremendous progress in the field of hormone action and consequent signal transduction. The 40th Colloquium Mosbach was devoted to the discussion of results concerning the molecular process of hormone action, especially the processes following hormone binding to the corresponding receptors. Structural and functional aspects of steroid hormone receptors as well as ion-channel-coupled and enzyme-linked receptors were treated in detail. Particular interest focussed on the latest results concerning transcriptional control, protein phosphorylation, the role of G-Proteins, oncogene proteins, involvement of phospholipases and the regulation of ion channels.