LY 43578 is an orally active aromatase inhibitor. LY43578 could inhibit O-demethylation of P-450-dependent p-nitroanisole and N-demethylation of ethylmorphine (IC50 of 0.3 and 5 μm, respectively) in rat liver microsomes. LY 43578 can be used to study neurological and cardiovascular diseases.