Receptors for γ-aminobutyric acid of the 'A' variety (GABA-A receptors), the most abundant inhibitory receptors in mammalian brain, are heteropentameric assemblies bearing multiple modulatory sites including the benzodiazepine (BZD) binding site. Ligands here can be agonists (positive GABA modulation, e.g., diazepam with anxiolytic but also sedative effects), antagonists, or inverse agonists (negative modulation). Partial agonists are desired for anxiolysis without side effects. We report a new structural class of high-affinity BZD site ligands—pyrido[1,2-a]benzimidazoles (PBI's), represented by prototype 1a (RWJ-16979). PBI compounds span GABA receptor activity from agonists to antagonists and include partial agonists with potential as novel anxiolytics. The PBI tricyclic nucleus was synthesized via benzimidazole formation, Dieckmann condensation, and amine reactions. Structural studies (¹³C NMR, X-ray) showed the keto tautomer predominates and the tricycle is planar. Biological testing: 1a had strong BZD affinity (IC₅₀ = 9.1 nM), GABA shift (GS) 1.5 (partial agonist), moderate anticonvulsant (ED₅₀ = 5.2 mg/kg ip in PTZ assay) and anxiolytic (MED = 10 mg/kg ip in conflict test) activity. 1b (4-ClPh) had GS 2.3 (full agonist), potent anxiolysis (MED = 1 mg/kg). Cycloalkyl analogs (1l, 1m) had GS 0.8-1.2 (antagonist) and antagonized chlordiazepoxide effects.