28 patients with primitive lung cancers were imaged by immunoscintigraphy (IS) with 111indium-labelled F(ab')2 anti-carcinoembryonic antigen (CEA), to assess this technique for mediastinal staging. IS revealed primitive tumours in 21 cases in whom mediastinal extension was assessed. There was concordance between clinical staging and IS confirmed by surgery in 17 cases, and discordance in 4. After surgery, discordance was in favour of IS in 2 cases (1 true positive and 1 true negative) and in favour of clinical staging in 2 (false positive of immunoscintigraphy). Anti-CEA IS could be useful for improving mediastinal staging of lung cancer.