In this study the level of adrenaline, noradrenalin, and vitamin A and E in plasma were investigated by High Performance Liquid Chromatography (HPLC) during the oestrus cycle in cows. At the beginning of oestrus cycle, adrenaline and noradrenalin levels of plasma were determined to be 19,4 ng/ml and 37,0 ng/ml (P<0.05), respectively. In the 13 th days of cycle, the levels of adrenaline 11,4 ng/ml and noradrenalin 26,2 ng/ml were found to be at minimum, then increased afterwards. The level of vitamin E was increased during the first ten days of cycle and then gradually decreased again. On the other hand, there was not any significant change in level of vitamin A content in plasma during the cycle.