In this study, the effects of nickel chloride (NiCl(2)) applied per os on testis histopathology and morphometry of mice were investigated. The metal was applied in pellets at a dose of 10 mg NiCl(2)/kg bw to male mice 4 weeks of age. After 3, 6, 9 and 12 weeks of nickel administration, the relative volume of whole seminiferous tubule, germinal epithelium, tubule lumen, interstitium and blood vessels as well as the diameter of seminiferous tubules were determined in the experimental and corresponding control groups. Microscopic examination of testis showed significant changes in all nickel-exposed groups. The degeneration of germinal epithelium, with released germ cells into the lumen of the tubules, and occurrence of empty spaces in the seminiferous epithelium were found in all experimental groups. The changes in the testes were time-dependent. The relative volume of empty spaces in the seminiferous epithelium significantly increased (P < 0.001) in all experimental groups when compared with the corresponding control. A significant decrease in the relative volume of seminiferous epithelium was observed after 6 and 12 weeks of Ni-exposure. The increased luminization of the tubules was found after 6 (P < 0.001), 9 (P < 0.01) and 12 (P < 0.001) weeks. Interstitial tissue significantly decreased after 6 and 9 weeks of Ni exposure and increased after 12 weeks of Ni intake. The seminiferous tubule diameter significantly (P < 0.001) decreased after 12 weeks. Results of this study report a serious, time-dependent changes in the testes, mainly in the germinal epithelium, after a peroral intake of nickel.