The aim of this study was to examine morphometric data of Leydig cells of 10 male chinchillas. Testes, cut into 5-microm thick sections, were stained using the p.a.S. and Masson's methods. Some 3800 Leydig cells have been evaluated. Their dimensions, as well as the diameters of their nuclei and the distances of the nuclei from the boundaries of the cells, have been measured. The areas of the surface and volumes of the nuclei of Leydig cells have been calculated, as well as the areas of the surface of the Leydig cells themselves. The following data have been obtained. The Nuclei of Leydig Cells. The largest diameters: longer cells - 12 microm; shorter cells - 10 microm. Mean diameters: longer cells - 5.67 +/- 3.44 microm, shorter cells - 4.45 +/- 3.44 microm. The largest surface area - 120 microm2, the mean surface area - 28.27 +/- 11.21 microm2. The largest volume - 1200 microm3, the mean volume of nucleus - 171.8 +/- 65.82 microm3. Mean distances of Leydig cell nuclei from the opposite boundaries of the cells amounted to 1.29 +/- 1.41 microm, 4.24 +/- 2.39 microm, 4.09 +/- 2.23 microm, 6.12 +/- 2.33 microm. Leydig cells. The largest diameters: longer cells - 24 microm, shorter cells - 22 microm. Mean dimensions: longer cells - 13.86 +/- 2.76 microm, shorter cells - 10.89 +/- 2.44 microm. The largest area of surface - 528 microm2, the mean area of surface - 155.44 +/- 59.78 microm2. Morphometric analysis confirmed cytologic observations that the shape of the nuclei of Leydig cells is somewhat ellipsoidal. The nuclei are located off-centre and are not situated in the greatest agglomeration of cytoplasm. The shape of Leydig cells is irregular. The obtained results may provide insight on the infertility of chinchilla males, as well as in research on the annual cyclic fertility of these animals. They may be put to use in practice for the purpose of improving breeding of this species.