Using a new stereological technique, the total number of nerve and glia cells can be estimated in selected brain regions. The method is completely independent of precise knowledge of nerve cell size, section thickness and of dimensional changes in brain tissue induced by histological procedures. It therefore provides an unbiased estimate of total nerve cell number. As an example, the total neuron number from the mediodorsal nucleus of thalamus in brains from schizophrenic patients is compared to control cases. The total neuron number was reduced by 40% in the brains from chronic schizophrenic patients.