Dicarba-closo-dodecaboranes (carboranes), which have spherical geometry and hydrophobicity, are applicable as a hydrophobic pharmacophore of biologically active molecules. We have investigated structure-activity relations based on the structure of the potent estrogenic agonist, 1-hydroxymethyl-12-(4-hydroxyphenyl)-1,12-dicarba-closo-d odecaborane, which we have previously reported. The geometry and separation distance of the phenolic and alcoholic hydroxyl groups play a critical role in the appearance of biological activity.