Biologically active oestrogen, estradiol-17beta, is an important se, Xenopus/Amphibian, hormone, but also makes an important contribution to the high concentrations of oestrogens which are present in malignant breast tissues. This antibody reacts with estradiol-17beta. No crossreactivity is seen with estrone, estriol, estrone sulphate, 16-ketoestradiol, 2-hydro, Xenopus/Amphibian,yestradiol,Porcinerogesterone, androstenedione, testosterone, or cortisol when measuring on tritium-labeled steroids in radioimmunoassay.