The paper describes the development of a conductometric biosensor for detecting trimethylamine (TMA) which is a good parameter for estimating fish freshness. The biosensor consists of two parts: a microconductometric transducer and a structured enzymatic membrane using a flavin-containing monooxygenase 3 (FMO3) which is known for its sensitivity and selectivity for TMA. The process parameters for the fabrication of the biosniffer and various experimental variables such as pH, time of exposure to glutaraldehyde vapour were investigated with regard to their influence on sensitivity and limit of detection. A low detection limit of 2 mu g/mL (ppm) and a linear range up to 40 mu g/mL (ppm) were obtained. 90% response was reached in less than 10 min. (c) 2007 Elsevier B.V. All rights reserved.