Alcohol increases estrogen signaling in mammary epithelial cells resulting in increased proliferation. We were interested in determining if PTHrP, a negative regulator of estrogen, could block the proliferative effects of alcohol. MCF-7 cells were treated with alcohol and/or PTHrP and proliferation was measured. Treatment of MCF-7 cells with alcohol caused an increase in proliferation whereas pretreatment with PTHrP inhibited these effects, suggesting that PTHrP may inhibit the growth-promoting effects of alcohol in the mammary gland.