Tobacco smoke has been implicated as a risk factor for breast cancer. We evaluated the effect of tobacco smoke condensate (TSC) on expression of the estrogen-inactivating enzyme SULT1E1 in the MCF10A human breast epithelial cell line. Because TSC contains components that are known aryl hydrocarbon receptor (AhR) agonists, effects of TSC treatment were compared to those of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and effects on SULT1E1 expression were compared to those on CYP1A1. Treatment for 24–72 h with 0.05–10 μg/ml TSC produced concentration-dependent increases in CYP1A1 mRNA content, decreases in SULT1E1 mRNA content, and increases in expression from a transfected AhR-responsive reporter plasmid. Treatment with 10 μg/ml TSC and 30 nM TCDD produced comparable increases in CYP1A1 mRNA levels (~300-fold) and decreases in SULT1E1 mRNA levels (~90%). Treatment with the AhR antagonist 3′-methoxy-4′-nitroflavone (PD168641, at 1 μM) completely inhibited TCDD-inducible CYP1A1 expression and partially reversed TCDD-mediated SULT1E1 suppression. PD168641 also inhibited TSC-mediated CYP1A1 induction and SULT1E1 suppression as indicated by rightward shifts of the TSC concentration-response curves. These findings support a role for the AhR in TSC-mediated regulation of CYP1A1 and SULT1E1 expression in human breast epithelial cells. Supported by NIH Grant (ARRA) R21ES016373 (to M.R.-M.).