Endocrine changes in cattle treated with GnRH. II. GnRH-stimulated LH and FSH secretion in cows with ovarian cysts in relation to the milk progesterone concentrations. The aim of the present investigation was to determine whether the LH and FSH secretion stimulated by GnRH of cows with ovarian cysts depends on the course of the progesterone concentrations. 18 cows with ovarian cysts were treated with 20 μg GnRH (Buserelin). At hourly intervals 8 blood samples were taken from each cow for the determination of LH and FSH. Progesterone concentrations were measured in milk samples, taken at intervals of 3 days until the 15th day following the application of GnRH. The cows were grouped according to the course of the progesterone concentrations. Cows with initially high progesterone concentrations released significantly more LH than the cyclic control cows. “Cystic cows” with initially low progesterone concentrations produced significantly less FSH than control cows. In conclusion, the above investigation indicates that there exists a relation between the LH and FSH secretion stimulated by GnRH and the course of the progesterone concentrations.