Intracellular signalling(or signal transduction)has been one of the most active research areas in biological science since early 80's. One of the major objectives of this research field is to understand the mechanism of an organism's response to stimuli from the environment.Recent research has focused on the biochemical and physiological changes in the cell following the initial transmembrane signalling event.The recent progress in this research area is briefly summarized with special emphasis placed on the newly proposed models for various intracellular signalling pathways in animal cells.