A probe type instrument to characterize tissue type that combines optical and electrical tests in a single device capable of providing data of both types almost simultaneously from very small, e.g. 3-10 mm diameter, areas of tissue surface. Key to this approach is an instrument capable of making almost simultaneous electrical and optical measurements on the same small areas of tissue, before being moved to scan adjacent tissue areas. In the preferred operation of the system fourteen measurement cycles are performed per second and each measurement involves a complex sequence of events, including (1) three optical and fifteen electrical tissue stimulations with subsequent detection, filtering and digitization of the tissue response; (2) extraction of specific parameters from the optical and electrical signals; (3) checking for errors, and subsequent classification of the extracted parameters into various tissue type categories; and (4) feedback to the system operator. Thus on the order of 15,000 measurements are made per one minute patient examination.