Serological tumor markers may become widely used as inexpensive and non-invasive methods of cancer detection. Markers of current interest for small cell lung cancer (SCLC) comprise enzymes, peptides, proteins, and carbohydrates. None of the serological markers for SCLC have yet proven to be of diagnostic value and at present their use is limited to monitoring disease and indicating prognosis. However, whilst serological markers related to the metabolic state of SCLC cells, such as neuron-specific enolase, serum thymidine kinase and tissue polypeptide antigen, may only be used for monitoring patients and for estimating prognosis, the other serological markers under current investigation may be used to indicate new treatment forms. Several novel approaches, including interference in the autocrine growth-regulating loop of SCLC by either peptides or antibodies, have been tried, SCLC is a highly heterogeneous tumor with respect to antigen expression, regulation of growth, and differentiation state. It is therefore important that new interventions are directed against both antigen-positive and antigen-negative tumor cells. For instance, radioisotopes or enzymes coupled to antibodies may be effective by exerting toxicity at some distance from the target. Antigens expressed on SCLC cells, such as peptide receptors involved in growth regulation, carbohydrate antigens like Lewis antigens, carcinoembryonic antigen and the ganglioside fucosylGM1, provide potential targets for antibody-conjugated therapy.