['Immunosuppression medications contribute to posttransplant diabetes mellitus in patients and can cause insulin resistance in male rats. Tacrolimus (TAC)-sirolimus (SIR) immunosuppression is also associated with appearance of ovarian cysts in transplant patients. Because insulin resistance is observed in patients with polycystic ovary syndrome, we hypothesized that TAC or SIR may induce reproductive abnormalities.', 'We monitored estrus cycles of adult female rats treated daily with TAC, SIR, and combination of TAC-SIR, or diluent (control) for 4 weeks. Animals were then challenged with oral glucose to determine their glucose and insulin responses, killed, and their blood and tissues, including ovaries and uteri harvested.', 'TAC and TAC-SIR treatments increased mean random glucose concentrations (P<0.05). TAC, SIR, and TAC-SIR treatments also increased the glucose response to oral glucose challenge (P<0.05). The insulin response to glucose was significantly higher in rats treated with SIR compared with TAC (P<0.05). TAC, SIR and TAC-SIR treatments reduced number of estrus cycles (P<0.05). The ovaries were smaller after SIR and TAC-SIR treatment compared with controls. The TAC and TAC-SIR treatment groups had fewer preovulatory follicles. Corpora lutea were present in all groups. Ovarian aromatase expression was reduced in the SIR and TAC-SIR treatment groups. A significant (P<0.05) reduction in uterine size was observed in all treatment groups when compared with controls.'] Do tacrolimus and sirolimus induce reproductive abnormalities in female rats?