Since the advent of the polymerase chain reaction in the mid-1980s, molecular diagnosis has become an important component of the services offered by many clinical laboratories. This presentation reviews selected applications of molecular methods in various sections and specialties of the clinical laboratory, and assesses the intellectual and technical qualifications and resources that traditional clinical laboratories can bring, and are bringing, to performance of molecular diagnostic tests. Special requirements for performance of molecular assays, in terms of both technical matters and clinical approaches, are also considered. Finally, attention is given to several contemporary factors that are tending to slow growth of molecular diagnosis in the clinical laboratory, and to other factors that are having a contrary effect, tending to promote growth in this area. A decision by an individual laboratory concerning the extent of its participation in molecular diagnosis should be based on recognition of the essential requirements for satisfactory performance of molecular testing, and a realistic appraisal of the laboratory's ability to meet these requirements.