A new interpretation of microvascular corrosion casting is described using examples from casts of the rat uterus taken during the oestrous cycle and early pregnancy. The casts are considered as representing a three‐dimensional model of the tissue vascular space; this characteristic model or tissue skeleton is used to demonstrate transient morphological changes that may be difficult to visualize by other techniques, that may be obscured by other structures, or destroyed by conventional aldehyde fixation procedures. This new application, when supplemented by conventional histology to determine vessel distribution within the tissue and to confirm observations first made by casting, provides a technique for visualizing three‐dimensional morphological changes in tissues that is accurate, relatively simple and far more rapid than the laborious method of histological serial sectioning and three‐dimensional tissue reconstruction.