The investigational psychopharmacologic drug candidate CP 615003 (NGD 91-3) is a potent subtype-selective partial agonist at the GABA-A receptor complex. It was designed to be fast acting without causing the sedation, memory impairment, addiction or potentiation of effects of alcohol associated with conventional anti-anxiety medication. Tissue distribution studies conducted during early clinical development of CP 615003 suggested limited brain penetration. In the Phase II clinical study, subjects tested at the high dose of NGD 91-3 showed a trend toward efficacy that did not achieve statistical significance.