The aim of the study was to investigate, if glyphosate, a common herbicide, affects the content of phytooestrogens in pasture grass, and if grazing on glyphosate treated pasture has effects on bovine reproduction. These kinds of signs had been detected in a case where cows escaped to a glyphosate treated pasture. The study consisted of three experiments. In the first one, grass samples collected from the pasture mentioned above were analysed for phytooestrogens. The second and third trials were grazing experiments on pastures treated with glyphosate. Oestrous behaviour of grazing cows and heifers were followed, and phytooestrogen contents of grass samples were measured. In the second experiment, cows were examined using transrectal ultrasonography, and progesterone was measured in milk samples. No effects on reproduction were found, and glyphosate treatment did not increase phytooestrogen content of grass. However, the results do not completely exclude the possibility that grazing on glyphosate treated pastures may have some influences on bovine reproduction in special circumstances or in certain plants. It seems to be, however, very unlikely in normal conditions.