Telepathology is the practice of pathology over a long distance. Components of a telepathology system include the following: a remote-controlled light microscope attached to a high-resolution video camera; a pathologist workstation incorporating controls for manipulating the microscope and a high-resolution video monitor; and a telecommunications linkage. An immediate challenge is to establish the specifications for a telepathology system. Breast tissue has served as a model. Receiver operator characteristic curve studies show that the pathologist's ability to discriminate benign from malignant breast tumors is similar using either a conventional light microscope or a video monitor with approximately 1000 lines of resolution. The percentage of cases for which pathologists render an "equivocal" diagnosis is the same for the two modalities. Telepathology may be an effective way to provide on-line consultations in difficult cases and to provide hospitals in remote areas with immediate access to anatomic pathology services.