The effect of hyperprolactinaemia on the prostate has still not been fully elucidated. The aim of the study was to estimate the influence of hyperprolactinaemia on expression of the androgen receptor (AR) in rat epithelial cells of the prostate lateral lobe and on the morphology of these cells. Studies were performed on sexually mature male Wistar rats. To provoke hyperprolactinaemia rats received i.p. metoclopramid (MCP). For light and electron microscopy the lateral lobes were obtained routinely. The intensity of the immunohistochemical reaction of AR (expression of AR) in the epithelial cells of the prostate lateral lobe was assessed by optical density measurements with the help of computer image analysis. Ultrastructural observations of the epithelial cells of the lateral lobe were carried out by means of transmission and scanning electron microscopes. The results showed a more than twofold increase in prolactin (PRL) concentration in the serum, but a twofold decrease in testosterone (T). The intensity of the immunohistochemical reaction of AR in the epithelial cells of the lateral lobe in the experimental group was higher than in the control group. We noted changes in the morphology of the epithelial cells of the prostate lateral lobe in the experimental group.