A total of 152 non-small cell lung cancers (NSCLC) were studied retrospectively to determine the relationship between epidermal growth factor receptor (EGF-R) status and the histological type, tumour size, nodal status and prognosis. EGF-R status was assessed on routinely embedded paraffin sections with an antibody to the cytoplasmic domain of the tumour (F4 antibody). EGF was demonstrated in all tumour types and every squamous and large cell carcinoma was positive for the antibody. Most tumours showed heterogeneity of staining. EGF expression was seen statistically more frequently in well differentiated tumours. Patients with 50% or more tumour cells showing positivity tended to have an improved survival but this result failed to reach statistical significance. There was no relationship between the size of the primary tumour or the lymph node status. Other cells, such as mucinous glands, bronchial epithelial cells and macrophages stained positively with the monoclonal antibody. EGF receptor status, with the antibodies presently available, adds little to help in either diagnosis or prognosis. Interpretation of data has to be guarded since the antibody was seen in some normal cells.