Anti-müllerian hormone (AMH) and androgenic steroids are key factors regulating the masculinisation of the internal and external genitalia during fetal development. AMH is produced in Sertoli cells and causes regression of the müllerian ducts in the male. 3 beta-Hydroxysteroid dehydrogenase (3 beta-HSD) is one of the key steroidogenic enzymes regulating testosterone production in Leydig cells. The objective of this experiment was to elucidate the development of the ovine fetal testes by identifying the spatio-temporal expression of AMH, 3 beta-HSD and androgen receptor expression within them. Fetuses from days 30 and 40 of gestation were fixed intact, while the gonads were dissected from the fetuses on days 70, 100 and 130 of gestation. Tissue was fixed in Bouin's fixative for 6 h, processed into paraffin wax and sections immunostained using rabbit anti-human AMH, 3 beta-HSD or androgen receptor antibodies. While seminiferous cords were absent on day 30 of gestation, pre-cord organisation was apparent and the gonad could be clearly distinguished from surrounding tissue by the presence of AMH and 3 beta-HSD immunopositive cells. Androgen receptor expression was not apparent at this stage. By day 40 of gestation the testis was organised into distinct seminiferous cords and intense immunostaining for AMH and 3 beta-HSD was present in Sertoli cells within the cords and Leydig cells in the interstitium respectively. Androgen receptor immunopositive cells were present in the interstititum but cells destined to develop into rete testis were immunonegative. By day 70 of gestation, the rete testis was organised in the centre of the testis and was strongly androgen receptor immunopositive. AMH and 3 beta-HSD expression was present in Sertoli and Leydig cells respectively. The expression of AMH, 3 beta-HSD and androgen receptor in the 100 and 130 day gestation fetuses was similar to that identified in the 70 day fetuses. In conclusion, Sertoli and Leydig precursor cells are present in the gonad prior to seminiferous cord formation and contain AMH and 3 beta-HSD at all stages of gestation examined. While androgen receptor immunoexpression was present in nuclei of interstitial cells from day 40 of gestation and in the rete testis from day 70 of gestation, Sertoli cells were immunonegative for androgen receptor at all of the stages examined.