A new route for operating affinity biosensors based on the voltammetric monitoring of the accumulated guest (analyte) is described. High sensitivity and selectivity accrue from the coupling of the specific receptor binding process and the inherent sensitivity of the preconcentration/pulse-voltammetric scheme. The redox (measurement) process results in dissociation of the receptor-guest complex, thus allowing multiple analytical determinations. The receptor layer also serves as an effective barrier that excludes interfering species. The new concept of preconcentration/voltammetric affinity biosensors is illustrated in connection with the detection of phenothiazine drugs using Langmuir-Blodgett films of their receptor, the enzyme tyrosine hydroxylase. The effect of various experimental variables upon the sensor performance is described.