1-Ethyl-2-(4-hydroxyphenyl)pyrrolo[2,1,5-cd]indolizine (NNC 45-0095) is a novel compound which represents the parent pharmacophore structure of a series of pyrrolo[2,1,5-cd]indolizine derivatives with mixed estrogen agonist/antagonist properties. NNC 45-0095 binds with high affinity to the estrogen receptor (IC50 = 9.5 nM) and exhibits full protection of bone loss in the ovariectomized mouse model for post-menopausal osteoporosis. (C) 2000 Elsevier Science Ltd. All rights reserved.