Ovulation requires coordinated maternal endocrine and oocyte-derived signals and appropriate gene expression in cumulus cells. We showed that the cumulus-oocyte-complex (COC) adopts a transient adhesive, migratory and matrix-invading capacity and proposed that the cumulus cells actively mediate ovulation. We now intend to determine the molecular mechanisms underlying this phenotype. The semaphorin family of guidance cues and their receptors play well-known roles in cell migration in a variety of cells. To-date, there has been no systematic evaluation of members of this family in the periovulatory ovary. Therefore, our aim was to evaluate the expression of semaphorin genes and their receptors in COCs and granulosa cells (GCs) over a periovulatory time course. Cells were collected from CBAF1 mouse ovaries at eCG + 0h, 4h, 8h, 12h or 16h post-hCG and analysed using RT-PCR. We also examined regulation of these genes in progesterone receptor null (PRKO; anovulatory) and heterozygous (PR+/-; normal fertility) mouse ovaries at 8h or 10.5h post-hCG. Class-3 semaphorins generally showed an induction in COCs and/or GCs by hCG, with most peaking at 8h post-hCG and returning to baseline by 12h. Interestingly, Sema3a, Sema3d and Sema3e had significantly higher expression in PRKO COCs compared to PR+/-. In contrast, Sema3g, Sema4d and Sema7a expression decreased in COCs as ovulation approached, but Sema7a was significantly higher in PRKO GCs compared to PR+/-. The A-class plexin receptors were generally induced by hCG in periovulatory COCs and were higher in PRKO COCs and/or GCs compared to PR+/-. Nrp1, the co-receptor for most class-3 semaphorins, was also induced by hCG and significantly reduced in PRKO GCs and COCs. Cumulatively, these results demonstrate that semaphorins and their receptors are expressed in a regulated manner in periovulatory ovarian cells, suggesting a role in regulating cumulus cell adhesion and repulsion properties during ovulation.