Whenever using modern stereological methods for estimating number-weighted or volume-weighted mean volumes of biological particles such as cell nuclei, either 'isotropic uniform random' (IUR) tissue sections or 'vertical' ones had to be used. However, with the currently available procedures and tools it was virtually impossible to prepare such sections from small specimens such as the mouse brain. Here, a modification of the 'isector' is presented, which allows the embedding of mouse brain halves into paraffin spheres as a useful basis for preparing IUR sections. By using this modified isector it could be shown for various types of neurons in the hippocampus and cerebellum of young adult mice, that there are no differences between estimated mean nuclear volumes obtained on IUR sections and those obtained on conventional frontal or sagittal ones. This result may be used to expand the interpretation of estimated mean nuclear volumes of the types of neurons investigated here.