PRX-00023, a serotonin 1A receptor agonist, was designed to provide high potency and selectivity for its target. To assess the possible therapeutic utility in anxiety, a randomized, double-blind, placebo-controlled trial was conducted in 311 subjects who met the criteria of the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, for generalized anxiety disorder. All subjects underwent a 1-week placebo run-in and were randomized to receive once-daily capsules containing either PRX-00023 (80 mg/d) or placebo for an additional 8 weeks. The primary outcome measure was the Hamilton Anxiety Scale (HAM-A). The Montgomery-Asberg Depression Rating Scale was used as a secondary endpoint to measure depressive symptoms. Statistical testing was performed with analysis of covariance, between baseline and week 8, with baseline values as a covariate. The anxiolytic effect of PRX-00023, compared with placebo, showed trends across all anxiolytic measures but failed to reach significance on the primary endpoint (HAM-A total score). Among the components of the HAM-A total score, the anxious mood item was significantly different from placebo in the PRX-00023-treated group (-1.015 vs -0.748; P = 0.02). The scores of the Montgomery-Asberg Depression Rating Scale were significantly improved compared with placebo at week 8 (-4.5 vs -1.6; P = 0.0094 in the last observation carried forward analysis). PRX-00023 was well tolerated; of note, there were no drug-related serious adverse events, and more patients discontinued due to adverse events in the placebo group (2.9%) than in the PRX-00023 group (1.4%). The most common adverse event was headache, observed in 15.7% and 10.9% of PRX-00023- and placebo-treated patients, respectively. Furthermore, there was no evidence of impaired sexual function, as measured by the Massachusetts General Hospital Sexual Function Scale. Collectively, these results support further clinical investigation of higher doses of PRX-00023 in anxiety and depression.