This paper describes a new methodology for three-dimensional (3D) representation of biological structures contained in a series of sections, using an illustrative example. Spatial reconstruction of a specific area of an astrocytoma biopsy was carried out with alignment of the serial sections at an accuracy of 0.01% (or 1 micro m cm(-1)), using the truncated pyramid representation (TPR) methodology. TPR includes: (a) serial tissue sectioning in a ribbon form; (b) alignment of the serial sections based on the properties of a 'truncated pyramid'; (c) identification and localization of structures in every section using a field frame, and representation of the contours of the structures in every section as topographic contours (charting); (d) artificial reconstruction of the missing space between serial sections, by drawing intermediate contours based on the prototype contours of successive sections in order to provide smoother and more elegant representation of the volumes (complementation); and (e) 3D reconstruction. Application of TPR in a selected area of the astrocytoma enabled us to observe the morphology and spatial distribution of neoplastic astrocytic nuclei, which encircled an adjacent blood vessel.