In common with other producers of fine chemicals, the pharmaceutical industry can deploy flow microreactors to provide a more flexible production regime than is achievable with large-scale batch reactors. With monitoring of output flow, microreactors can be adjusted exquisitely to give enhanced and inherently safer protocols. Bulk production can be achieved through long run times or parallel reactors. However, microreactors can also be used advantageously in pharmaceutical R&D in other ways. This paper describes their use in the creation of a tool for rapid discovery and optimisation of leads to new drugs. Here microreactors are used to create an integrated micro-scaled chemical synthesis and bioassay system able to conduct fast-cycling iterative searches of diverse chemical space as an enhanced method for identifying and optimising novel lead chemotypes. The use of a microreactor to provide point-of-use access to PET ligands is also described. This significant down-scaling and acceleration of the synthesis of potent but short-lived biomarkers of disease could provide a means of significantly shortening the time and resources required to achieve a drug approval.