Studies were carried out on lipid and lipoprotein fractions in the serum of cows during summer and winter feeding. The experimental group comprised 32 Black-and-White cows in the final stage of pregnancy (2-3 weeks before calving) or in the 6^th week of lactation. Total serum lipid (2.51 g/l) and cholesterol (2.51 mmol/l) concentrations were significantly lower (P<0.01) in cows subjected to drying than in lactating animals (3.29 g/l and 3.86 mmol/l, respectively), irrespective of the feeding period. In contrast, the serum triglycerides concentration was 0.34 mmol/l in cows before calving and twice as high than during lactation. It was also shown that HDL constituted the main fraction, and that HDL in cows prior to calving represented about 74% of serum lipids, increasing to about 80-85% during lactation. The LDL concentration was lower, representing, on average, 22% in dry cows, and 13-15% in the 6^th week of lactation. Prior to calving, triglycerides represented over 40% of LDL, 32% was represented by cholesterol. In the peak of lactation the TG fraction in LDL decreased to 14-19%, while that of cholesterol increased to over 45%.