AbstractNineteen structural analogues of γ‐aminobutyric acid (GABA) and the anxiolytics buspirone and diazepam were tested for their ability to modify GABA function in vitro. Each compound was added to the GABA receptor binding assay, the flunitrazepam receptor binding assay, the sodium‐dependent GABA binding assay, and the assay for GABA aminotransferase. It was anticipated that some of these analogues would substantially affect several of these assays. The most interesting compound to emerge was phenylthiohydantoic acid. This not only inhibited GABA receptor binding (Ki= 121 μM) but also stimulated flunitrazepam binding and inhibited the activity of GABA aminotransferase. In light of the evidence that a reduced GABA function can be a factor in anxiety, phenylthiohydantoic acid has the potential to be a GABA‐mimetic and thus be useful in the treatment of