Mature epithelial cells derived from the sputum of normal healthy adults lack GB, while the epithelial cells of sputum collected from patients with lung tumours contain a spectrum of epithelial cells with active GB, some of which are clearly tumour cells, based upon their morphology. The presence of abnormal epithelial cells was confirmed by the cytologist whilst observing the fluorescent stained cells and later by independent cytological analysis of these same cells employing conventional stains.