The segmentation of scenes of fixed tissue sections for quantitative histopathology is the crucial step for further image processing. Different segmentation methods for the separation of nuclei, nucleoli and whole cells in methacrylate-embedded sections of rat liver were investigated. Reasonable segmentation results were obtained using a contrast-enhanced polar-coordinate transformation to distinguish nuclei, a compactness algorithm to distinguish nucleoli and a skeletonization algorithm to delineate cells when a priori information on the morphometric and photometric properties of the liver tissue was included.