Successful drug discovery and development depends not only on proper target selection and lead generation/optimization but also on defining appropriate clinical endpoints ('biomarkers') for evaluation of drug candidates in humans. Clinical trials of new chemical entities or biologics are faced with the challenge of setting criteria of efficacy in slowly developing, multi-factorial diseases without rendering such trials unmanageable and extremely expensive. Most of the major diseases in the western world today are chronic, slowly developing disorders with a significant life style or environmental component. Early biochemical markers of disease processes are thus critical in diagnostic and therapeutic decision-making processes in light of evaluating new drugs against some of the major diseases. Rapid, sensitive and inexpensive read-out systems using lab-on-a-chip approaches are promising developments. Furthermore, biosensors, systems that measure, alert and trigger a response on or in the body, are bridging the gap between diagnosis and treatment.