An octopine sensor was developed which was based on the immobilized enzymes pyruvate oxidase and octopine dehydrogenase. The sensor consisted of a reactor ox):gen electrode, flow cell, peristaltic pump, recorder, and a buffer tank. The optimum conditions for the sensor were as follows. pH 7.4; temperature, 26 degrees C; Slow rate, 0.77 ml min(-1); sample volume, 50 mu l; and 0.05 M phosphate buffer transfer solution. A good correlation was obtained between the octopine contents in scallop adductor muscle determined by the sensor and those determined Dy high performance liquid chromatography (HPLC). These results show that scallop freshness can be estimated by the determination of octopine using the proposed sensor system.