[en] The neural mechanisms controlling mate recognition and heterosexual partner preference are sexually differentiated by perinatal actions of sex steroid hormones. We previously showed that the most important action of oestrogen during prenatal development is to defeminise and, to some extent, masculinise brain and behaviour in mice. Female mice deficient in alpha-foetoprotein (AFP) due to a targeted mutation in the Afp gene (AFP-KO) do not show any female sexual behaviour when paired with an active male because they lack the protective action of AFP against maternal oestrogens. In the present study, we investigated whether odour preferences, another sexually differentiated trait in mice, are also defeminised and/or masculinised in AFP-KO females due to their prenatal exposure to oestrogens. AFP-KO females of two background strains (CD1 and C57Bl/6j) preferred to investigate male over female odours when given the choice between these two odour stimuli in a Y-maze, and thus remained very female-like in this regard. Thus, the absence of lordosis behaviour in these females cannot be explained by a reduced motivation of AFP-KO females to investigate male-derived odours. Furthermore, the presence of a strong male-directed odour preference in AFP-KO females suggests a postnatal contribution of oestrogens to the development of preferences to investigate opposite-sex odours.