On-line tests with Pseudomonas fluorescens HK44 were carried out using a biosensor system with a flow-through cell and sample injections to detect low concentrations of naphthalene. Kinetic experiments permitted a 19 min response time and definition of a 50 min induction period for bioluminescence assays. A mathematical model showed that 0.2 g/l is the best cell concentration to be used in the detection of low naphthalene concentrations, with the highest acceleration rate of bioluminescence sensitivity increase (0.46 nA l/(g min(2))). Calibration curves with different concentrations of naphthalene showed a linear correlation up to 0.4 mg/l (3 muM) corresponding to 211 nA output signal. The lower limit of naphthalene detection by strain HK44 was in the region of 0.02 mg/l (0.16 muM), below the naphthalene health advisory limit for drinking water consumed over a lifetime suggested by EPA. (C) 2003 Elsevier Ltd. All rights reserved.