The development of high and intermediate voltage electron microscopes provides the ability to investigate the ultrastructure of thick biological samples. This produces a unique view of the 3-D interrelationships of cells and organelles. However, the analysis and display of this 3-D information has presented challenges, particularly to quantitative biologists. Major advances in adapting computed tomography (CT) to electron microscopy have provided the major means of 3-D analysis of cellular ultrastructure (1,2). In particular, tremendous gains in determining the structure of macromolecules have occurred with advances in electron microscopy CT (3). However, CT remains an arduous undertaking and one not well suited to analysis of the structural alterations within large populations of cells requiring many reconstructions. We have adapted an alternative approach, Tuned Aperture Computer Tomography (TACT®), for use with high and intermediate voltage electron microscopes. Although with EM specimens TACT® does not usually produce as high Z axis resolution as CT, the simplicity of the TACT® algorithms lend themselves to the rapid analysis of multiple samples. TACT® is already gaining acceptance in radiology (4, 5). Like CT, TACT® uses a series of images of the sample taken from different angular perspectives. However, unlike CT, for TACT® only a few projections are required and thus good reconstructions of beam sensitive material are possible. The quality of the reconstruction is determined by the quality of the input images, the total angular spread, and the individual tilt increments between images. Better images, a greater angular spread, and smaller angles between images will produce more accurate results.