In AHR-responsive B6 mice, TCDD and DMBA can influence mRNA expression involved with mammary gland differentiation as well as genes involved with AHR ligand and estrogen metabolism; because D2 mice express the low-affinity AHR but are susceptible to diet-induced obesity, we further examined whether HFD-fed D2 mice exposed to TCDD and/or DMBA would be responsive to AHR-ligand–induced expression changes. This evidence concerns the gene AHR and obesity due to melanocortin 4 receptor deficiency.