Proficiency testing programmes for measuring screening skills in pathology are mainly conducted using conventional glass microscope slides. However, the availability of robotic microscopes allows an entire conventional slide to be digitized. Our experiments have shown that, using a widely available robotized microscope and a PC, the image of a single field may be acquired in 2 s on average, including stage movements, autofocus and storage. Digitizing an entire slide, a fully automated procedure, takes up to 8 h. If the image of each field is compressed at an appropriate quality level (a compression ratio of, say, 35:1) it requires about 40 kByte to be stored, resulting in a total storage requirement of about 600 MByte per slide. Thus one CD-ROM can be used to store one virtual slide, as well as a self-installing program to provide a microscope simulator facility. This allows pathologists to examine the virtual case from their computer in a similar manner to looking at a glass slide on a conventional microscope. This permits a new, computer-based approach to proficiency testing in histopathology and cytopathology. Use of virtual slides should encourage the diffusion of national quality assurance programmes, which at present suffer from certain organizational and logistical limitations.