In previous studies, carried out in humans, we showed that females are resistant to Leishmania mexicana infection. We also showed that 17β-estradiol (E2) induces killing of parasites inside of murine macrophages. In this work, we compared, for the first time, L mexicana survival inside of male (male BMDM) and female (female BMDM) bone marrow-derived macrophages (BMDM) treated in vitro with E2 or dihydrotestosterone (DHT). We also compared their levels of nitric oxide (NO), interleukin (IL)-6, IL-10, IL-12p70 and tumour necrosis factor (TNF-α). We found that female BMDM are a lot less susceptible to infection as compared with male BMDM. 17β-estradiol induced killing of most parasites inside of female BMDM. Dihydrotestosterone, on the other hand, induced some parasite killing inside of some infected male BMDM. Interleukin-6 levels were higher in female BMDM treated with either hormone. Neither TNF-α nor IL-10 levels showed significant differences compared with sham controls. Interestingly IL-12p70 was more abundantly produced by sham female BMDM as compared with sham male BMDM. Only female BMDM treated with E2 trigger a robust IL-12p70 production, but it was significantly reduced in male BMDM. This suggests IL-12p70 is an important factor in female-macrophage resistance to L mexicana parasites.