The conventional detection methods for neurotransmitter /spl gamma/-aminobutyric acid (GABA) are concentrated on HPLC and enzymatic reactions. We report here a novel acoustic immunosensor for dynamic measurement of GABA in buffer solution using an immunohistochemical strategy. The adsorption process of anti-GABA on a well-defined gold electrode surface of a quartz crystal and the immuno-interaction between GABA and anti-GABA in liquid were monitored. Real time measurements of changes in the resonant frequency and electrical equivalent circuit parameters of the quartz crystal were used to monitor the above two processes. The resonant frequency changes of the quartz crystal were a direct indicator of change in mass of the quartz crystal. The electrical circuit parameters were used to analyze the changes in the interfacial viscoelastic properties of anti-GABA adsorption in air and GABA binding in liquid. It was found that water plays a critical role in antibody immobilization process. The proposed immunosensor can detect the concentration of GABA down to 38.0 /spl mu/M in buffer solution. Further, it showed no response against common interferents in brain, like L-aspartic acid, L-glutamine, L-alanine, 5-aminovaleric acid, glycine, (s)-(+)-2-aminobutyric acid. We conclude that this sensor will find potential application in real time monitoring of GABA.