To characterise the effects of obesity on endogenous oestrogen, and its contribution to PAH, the effects of an aromatase inhibitor, ANA, and the CYP1B1 inhibitor, 2,2′,4,6′-tetramethoxystilbene (TMS), were studied in obese mice. The gene discussed is CYP1B1; the disease is obesity due to melanocortin 4 receptor deficiency.