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For the study of the length of seminiferous tubules and the volume of Leydig cells, forty-three Sprague-Dawley rats were sacrificed. Fifteen-week old rats were used as the control and eighty-week old rats as the experimental groups. The volume of each testis was measured by the Archimedes principle, and the experimental group was divided further into the three subgroups: bilaterally non-atrophied, unilaterally atrophied and bilaterally atrophied groups. Each of the testes was fixed in Bouin’s solution for 18 hours, and the 5㎛-thick sections were stained with Masson’s trichrome stain. For the determination of the tubule length, a light microscope with an eyepiece disc containing 100 graticules per unit area and an eyepiece micrometer disc was used for counting the numbers of tubule cross sections, for measuring the tubule diameter and for calculating the proportion of tubule under 100 times magnification. For the estimation of tubule length, VtN method (Lennox et al., 1970) and volume/area method (Bascom and Osterud, 1925) were applied, and for the determination of Leydig cell population, a light microscope with an eyepiece disc containing 441 points per unit area was used for counting the Leydig cell proportion under 400 times magnification. Point counting method (Chalkley’s method modified by Lennox and Logue, 1979) was applied for calculation. The findings were summarized as follows: 1. In comparison with the control group, the atrophied testes showed degenerative changes of the seminiferous tubules and increased interstitial space. 2. The volume of atrophied testes of eighty-week old rats significantly decreased in comparison with the control. 3. The total length of seminiferous tubule of the bilaterally atrophied testes of eighty-week old rats significantly decreased in comparison with the control. 4. The proportions of Leydig cells in the testes of eighty-week old rats significantly increased but the total volume of Leydig cells were not significantly changed. These results showed that the atrophied testes by aging had shortened seminiferous tubules, but there were not any changes in the volume of Leydig cells.
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