A computer system has been developed which allows both mapping and planimetry of histological preparations. Data consist of cytoarchitectonic boundaries defined in low-power micrographs of thick sections, and nuclear and vascular profiles defined in high-power micrographs of semi-thin sections taken from the original thick tissue, and landmarks common to both. Data from these different preparations and magnifications are entered into the computer on a digitizing tablet and are stored as points in a real-world coordinate system, along with profile labels, landmarks for alignment purposes, and section depth. Subsequent programs determine parameters such as area and perimeter for each profile, as well as its geometric center and relationship to the cytoarchitectonic boundary. This mapping parameter allows morphometric analysis of profiles as a function of their position. Other programs allow display and manipulation of data in 3 dimensions, cell counts, and stereology. Data acquisition is done in the laboratory, using a micro-computer; analysis and display are done on a large time-sharing computer connected to the small machine by a telephone interface.