Blood samples were taken from 134 Holstein cows between day 20 to 100 postpartum to determine the concentration of urea, cholesterol, glucose and total lipids and to define their relation to the reproductive performance traits: interval (I), service period (SP) and insemination index (II). Investigations were carried out in monthly intervals from October 1996 to October 1997. Average values of plasma urea, total lipids, cholesterol and glucose for the entire period studied were 5.78 mmol.1⁻¹, 3.61 g.l⁻¹, 3.34 mmol. l⁻¹ and 3.61 mmol. l⁻¹, respectively. High concentration of blood urea was related negatively with the value of the insemination index (rp = -0.51). When the average concentrations of total lipids were low in plasma in the specified time (month) negative correlations were found between total lipids and the length of service period (rp = from -0.23 to -0.54) and value of the insemination index (rp = -0.42). The concentration of plasma total lipids increased in time from post partum. Traits of reproductive performance were affected by the internal environment. Especially negative influences were observed when the concentration of plasma urea as well as total lipids and cholesterol increased or decreased abnormally.