Perspective on the discovery and scientific impact of p38 MAP kinase.

It has now been almost 20 years since the discovery of p38 MAP kinase and its role in inflammatory cytokine synthesis through reverse pharmacology and its subsequent exploration as a potential target for autoimmune and other diseases. At the time of its discovery, the use of cell-based phenotypic screens to identify new molecular targets was at its infancy, and while p38 MAP kinase was not the first target to be identified this way, it provides a useful model for reviewing the pros and cons of this approach and the subsequent impact it can have on discovering new medicines.