INTRODUCTION: Reproduction traits play a very important role in animal production. Several polymorphisms affected proliferacy, ovulation rate, sterility, alive birth, shorter weaning-to-oestrus intervals, stillbirth, embryonic survival rate and unfertilized ova ratios have been described so far in several genes (e.g. GDF9, BMP15, BMP1B, EST1, PRLR). Among them BMP15 (growth and differentiation factor 9B an X-linked gene) has been shown to play a crucial role in ovarian regulation THE AIM OF STUDY: The aim of the presented study was to determine the expression pattern of BMP15 in growing equine follicles during the long day period.