The EMI general Purpose Scanner is briefly described, with particular reference to the use of window height and window width variations. Patient preparation in relation to movement artefacts and contrast medium is considered, and a method of localization of tomographic sections is described. The Scanner produces brain examinations of high quality. Because a head water bath is no longer required, the base of the skull can also be examined. In the thorax computerized tomography is particularly valuable in showing pleural disease in the forms of thickening, plaques or tumours, and in demonstrating retrosternal lymph node enlargement. Small peripheral metastases can be identified when not shown by conventional tomography. In the abdomen lymph node masses, retroperitoneal tumours and pancreatic disease has been identified, often more completely than by other methods, or where other methods have failed. This has proved particularly valuable in the grading of malignant disease and in the monitoring of subsequent treatment. It is particularly helpful in the planning of radiotherapy. Metastases in liver and bone can be clearly defined when still quite small (0-5.1 cm), but comparison with other methods of diagnosis such as grey scale ultrasound and isotope scanning will be needed before the role of computerized tomography in evaluating these lesions is known.