ERB-79 is a synthetic estrogen and a selective agonist of the ERò. It is a racemic mixture, with the active enantiomer being ERB-26. ERB-79 shows more than 484-fold selectivity for transactivation of the ERò over the ERñ. Its EC<sub>50</sub> value for the ERò is 0.448 nM (14.52% of the potency of estradiol) and for the ERñ is 79 nM (0.03% of the potency of estradiol). It has no antagonistic activity at either receptor. ERB-79 is active in preclinical models of arthritis. The chemical structure of ERB-79 does not appear to have been disclosed.