Over the past decade the use of monoclonal antibodies has greatly advanced our knowledge of the biological properties and heterogeneity that exist within human tumours, and in particular in lung cancer. Early studies suggested that both the lack of specificity of individual antibodies and heterogeneity in antigenic expression would limit their widespread application in clinical practice. However, improvements in antibody selection techniques and a greater understanding of the epitopes detected with these antibodies have slowly led to the development of antibodies with improved specificity. While preliminary studies of the immunohistology of lung cancer suggest that these antibodies may be of value in histologic typing, predicting chemosensitivity and detecting bone marrow metastases, larger clinical trials are required before immunohistology becomes standard clinical practice in lung cancer studies. With such studies it is likely that the role of lung cancer immunohistology will become better defined. It is also certain through our greater understanding of lung cancer biology and heterogeneity that monoclonal antibodies will in the future play a major role in imaging diagnostic techniques, and in specific targeted therapies where antibodies directed against autocrine growth factors or their receptors, oncogene protein products, or conjugated with pharmacologic agents may replace the highly toxic, non-specific chemotherapeutic approaches of today.