The effects of long-term adrenalectomy (ADX) on hippocampal neurones were investigated 5 months after surgery in male Sprague-Dawley rats. Cells in Nissl-stained sections from ADX rats were counted and compared with those in sections from sham-operated rats. The ADX rats had a significantly reduced number of dentate granule cells. A novel finding was a significant reduction in the number of pyramidal cells in CA1, CA2, CA3 and CA4 regions of the hippocampus. Thus long-term adrenalectomy causes loss of dentate granule cells and pyramidal neurones of the hippocampus.