Implementation of a Vicom-VME image processing workstation for the frameless stereotactic operating microscope system has allowed an improved interpolation algorithm for more accurate reconstruction of three-dimensional data, the integration graphically of multimodality imaging information, an additional stereotactic graphics display outside of the microscope optics and optional three-dimensional displays through communication with a Convex mini-supercomputer. A precision-milled coupling for reproducible attachment of the spark gap bracket to the microscope has eliminated the need for that transformation calculation during each case. Clinical utility has been greatest in providing navigational guidance to small subcortical or deep lesions and in defining the extent of preoperatively planned resection of larger, infiltrating tumors. Mean accuracy in the past 17 cases has been 3.5-6.5 mm. The frameless methodology has also enabled extracranial stereotactic surgical procedures in 7 patients.