Three feeding groups were used: the control (SOY) was fed diets without rapeseed products, and the two experimental groups were fed with either 10% rapeseed meal (RSM) or with 12% OO rape seeds (PFRS). Half of the boars from each group were slaughtered after 1 or 2 years. In RSM and PFRS boars steroid-3-beta-ol-dehydrogenase activity was high, whilst Leydig cells were not numerous after 1 year. Degeneration and necrosis of seminiferous epithelium resulting in atrophy of seminiferous tubules appeared in RSM boars after 2 years. In the PFRS group the lesions were stronger and proliferation of Leydig cells with high steroid-3-beta-ol-dehydrogenase activity was observed. In 1-year-old RSM and PFRS boars there were foci of necrosis in the epididymal epithelium. Thyroid weight in RSM boars and liver weight in PFRS boars were distinctly higher only during the first year. In these thyroid glands flattening of glandular epithelium and enlargement of colloid masses were observed, while in the livers, parenchymatic degeneration and structural transformation appeared. Testis weight increased after 2 years in RSM and PFRS boars; however, this had little effect on semen production.