Carnosinase activity was determined in uterus extracts of sexually immature sows, on particular days of the oestrous cycle, and on the 20th and 30th day of pregnancy. In mature sows carnosinase activity in the uterus was on the average 4.5 times higher than in immature sows. Activity of the enzyme in the oestrous cycle increased from the zero day (first day of the heat) until 13th day, followed by a rapid decrease, reaching the lowest levels on the 17th day of the cycle (3 times lower on the average than on the zero day). On the last days of the cycle (20-21st) activity of carnosinase reached again levels similar to those of the zero day. Carnosinase activity in a uterus corner of pregnant sows (20th day of pregnancy) was over 4 times higher than in the "peak" day of the oestrous cycle (13th day), and over 12 times higher than in immature sows. Activity of the enzyme increased along with progressing pregnancy. It was found that activity of carnosinase in uterus corner of swines was related to the level of progesterone determined by other authors in the blood plasma.