The effects of a combination of aminoglutethimide (AG) 1,000 mg daily and 4-hydroxy-androstenedione (4OHA) 500 mg i.m. weekly on peripheral aromatase activity as measured by in vivo radioisotopic tracer methodology and serum oestrogen suppression were investigated in ten post-menopausal women with advanced breast cancer. This evidence concerns the gene CYP19A1 and breast carcinoma.