['In utero and lactational 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure causes lobe specific inhibition of prostate development in C57BL/6 mice due primarily to region specific inhibition of prostatic epithelial bud formation by the urogenital sinus (UGS). This inhibition requires that the receptor for TCDD, the aryl hydrocarbon receptor (AhR), must be present. We tested the hypothesis that TCDD inhibits prostatic epithelial bud formation by acting directly on the UGS.', 'UGSs were removed from WT and AhR null mutant (AhRKO) male C57BL/6 mice on gestation day 14 and incubated in vitro with vehicle, 10-8 M testosterone or 10-8 M testosterone plus 10-9 M TCDD for 5 days. Budding was evaluated by a newly developed technique, namely scanning electron microscopy of UGS epithelium after removal of UGS mesenchyme.', 'Few buds were present in UGSs of either genotype in the absence of testosterone, while many were observed when testosterone was present. TCDD prevented prostatic epithelial buds from forming in UGSs from WT mice but it had no effect on UGSs from AhRKO mice.'] Does 2,3,7,8-tetrachlorodibenzo-p-dioxin inhibit prostatic epithelial bud formation by acting directly on the urogenital sinus?