Small cell lung cancer (SCLC) comprises a significant fraction of all lung cancers; it is most frequent in women, where it represents up to 25% (1 ). It is characterized by neuroendocrine differentiation, with immunohistochemistry for certain neuroepithelial markers used in diagnosis to differentiate SCLC from other types of lung cancer. We have evaluated the use of reverse transcription polymerase chain reaction (RT-PCR) for selected neuroendocrine markers as a way to specifically detect SCLC cells in (1) surgical, postmortem or bronchoscopic biopsies and (2) the peripheral blood or lymph node aspirates from SCLC patients. Products are detected either directly by ethidium bromide staining of agarose gels or, with enhanced sensitivity, by transfer to a membrane followed by hybridization with a specific radiolabeled probe.