A novel series of 4-amino-pyrido[2,3-b]indoles is presented as GABAA modulators with good potential as therapeutic agents for the treatment of anxiety disorders.Benzodiazepines exhibit a wide range of pharmacological actions, including anxiolytic activity, which are mediated by specific high affinity receptor sites in the central nervous system (CNS)I. The benzodiazepine (BDZ) receptor is one constituent of a supramolecular complex which also contains separate, but allosterically coupled, recognition sites for γ-aminobutyric acid (GABA) and barbiturates. The oligomeric units of this GABAA/BDZ-channel complex form a drug and transmitter controlled chloride channel2,3. Despite advances made in terms of molecular characterization, the search continues for selective anxiolytics which are devoid of the unwanted side-effects typical of BDZs such as ataxia, sedation and interaction with ethanol.Literature studies4 indicate that [35S]-t-butyl-bicyclophosphorothionate (TBPS) binds with high affinity to the GABAA complex when the chloride channel is in the closed state but with low affinity when in the open state. Compounds can, therefore, inhibit high affinity binding either by competitive displacement (e.g. picrotoxin) or by shifting the channel to the open state, which appears to be the case for the currently described series of pyrido[2,3-b]indoles (α-carbolines). In contrast, potentiation of binding can occur by a shift towards the closed state of the channel. For example, it has been demonstrated5 that both foot-shock stress and anxiogenic β-carbolines increase [35S]TBPS binding.The effect of compounds on [35S]TBPS binding appears to parallel chloride conductance and gives a measure of drug efficacy in terms of permeability of the chloride channel6. Since anxiolytics, which act at the GABAA complex, are thought to act by promoting GABA-induced chloride conductance, the effects on TBPS binding have been used to predict potential anxiolytic activity of our compounds. In addition, direct interaction at the BDZ site of the complex was investigated using [3H]-flunitrazepam binding7.