In situ PCR is a new and exciting technology that is already providing a mechanism to gain insights into disease pathogenesis. As with other emerging technologies, its true strengths and weaknesses are becoming clearer with time.In situ PCR encompasses several different techniques, not all of which are equally applicable to different starting materials. It appears to be most effective for low-copy DNA or RNA detection in single-cell preparations after controlled fixation and pretreatment. However, the exact quantification of results still remains somewhat problematic. Directin situ PCR yields significantly less specific results than indirectin situ PCR and is— with currently used protocols—not applicable in tissue sections. Protocols need to be improved significantly to render them applicable to routinely processed specimens. Clinical application of this technology in routine laboratories must await resolution of its current limitations. Its impact in endocrine pathology will be most marked where conventional ISH fails owing to low sensitivity. It is also reasonable to believe that other methods, such as the self-sustained sequence replication (3SR) [14] or refined ISH procedures, may soon become suitable for studies on archival materials.