AbstractIn this article four cases of signal transduction in biology are discussed, ranging from a case which we do understand in molecular detail (genetic induction) through two cases where the fog may be beginning to clear (vertebrate vision and bacterial chemotaxis) to a case where we are still struggling to define the participants of the play (the avoidance response of the fungus Phycomyces).—Although most of the facts presented are not brand new, the juxtaposition of them is perhaps unconventional and may be of interest at least by way of outlining an area of research of some promise. No doubt modern concepts and technologies of chemical and physical research will play a great role in this borderline area between a variety of fields, presenting great challenges to the ingenuity and versatility of the experimente