Abstract Although much is known about the biology of vascular endothelial growth factor (VEGF) and its receptors, little is known about the role of the VEGF receptors neuropilin (NRP)-1 and NRP-2 in the process of bovine follicle development. The aim of the present study was to examine the hormonal regulation of NRP-1 and NRP-2 mRNAs by real-time PCR in follicles from the bovine ovary and in cultured granulosa cells. The NRP-1 gene was expressed in the granulosa and theca cells in the post-selection (POF) and pre-selection (PRF) follicles in the bovine ovary. In contrast, the NRP-2 gene was expressed only in the theca cells in the POF and the PRF. The level of NRP-1 mRNA was significantly increased by treatment of the cultured granulosa cells with 10 ng/ml estradiol (E2). In contrast, the addition of progesterone (P4) to the culture medium decreased the expression of the NRP-1 gene. The level of NRP-1 mRNA was increased by 10 ng/ml E2 with or without 1 ng/ml P4, but the level of NRP-1 mRNA was decreased if the P4 level was increased to 10 ng/ml, even when 1 ng/ml E2 was also added. Follicle-stimulating hormone did not stimulate the expression of the NRP-1 gene. These results are the first data showing that NRP-1, but not NRP-2, is expressed in the granulosa cells of bovine follicles and that NRP-1 gene expression is regulated by sex steroids. Our findings suggest the involvement of NRP-1 in follicle development in the cow.