Metabolism of lipids and their level in blood of animals and men is dependent on many factors, including the stages of estrus cycle. The aim of this study was to establish the level of triacylglycerols (TG) and cholesterol in blood plasma during the periovulatory period in mares. 12 Arabian mares were included in the investigation during the breading season. The number of days of estrus cycle was defined on the basis of results of transrectal ultrasonography conducted once a day. The animals were divided into two groups: 8 mares with recorded ovulation and 4 with anovulatory cycle. Blood samples were collected from jugular vein at rest in the morning, and plasma TG and cholesterol levels were determined by enzymatic methods. In blood plasma of ovulating mares the levels of TG and cholesterol decreased after ovulation. In the group of anovulatory mares the values of measured parameters were not statistically different.