Two herds of Black-White cows with different level of milk production were studied. Irrespective of milk yield all cows were milked three times a day. Milk of low production herd was characterized by 4,31% of fat, 3,46% of protein and 16,52 mg/100 ml of urea. Urea level in high milk production herd reached 25,55 mg/100 ml but content of fat (4,28) and protein (3,22) was lower. The highest level of urea during summer season was observed in milk from afternoon milking and there was 6 mg/100 ml difference in comparison to morning milking. The same pattern of daily differences in milk composition was found during winter season. The lowest values of milk urea were observed in late summer and winter seasons. Urea spring season values were over 30 mg/100 ml (milk yield > 20 kg). High level of urea and low protein content in the milk of high yielding cows indicated large energy deficiency while there was surplus of crude protein in feeding ration.