This article applies the lens of the knowledge exploration/exploitation dilemma to the renewal of Celltech Plc. From a theoretical perspective it has often been argued that as a firm matures, exploitation of current organizational knowledge drives out exploration of new ideas, and that this increases the likelihood of firm failure. This same literature gives few clues as to how balance can be maintained, or decline reversed. Our case study documents the decline of Celltech, its rejuvenation from near bankruptcy in 1990, and its subsequent ability to prosper to become the eighth largest biotech firm in the EU in terms of market capitalization. Through the Celltech case we show empirically that renewal based on exploration is possible even in a firm where exploitation has come to dominate. This case also illustrates how a balance between exploration and exploitation can be maintained for over half a decade, despite the theoretical tendency stated in the literature for exploitation to dominate. We offer insights into the process of maintaining a balance, including reorganization to release internal diversity to stimulate exploration, creation of a common language, and building systems to institutionalize the maintenance of a balance between exploration and exploitation.