[en] The e-nose technology has enormous potentialities for in site monitoring of off-odours. However a number of limitations are associated with the properties of chemical sensors, the signal processing performances and the real operating conditions of the environmental field. The field experience of the research group included testing of a large amount of sensors in different sensor technologies and among those the metal oxide-based gas sensors (Figaro type) are the best gas sensors for long term application, as stated during more than 1 year of field testing. To be usable for the off-odours field measurement, the e-nose has to deal with the lack of long term stability of these sensors. The drift and the sensors replacement have to be considered. In order to appraise the time evolution of the sensors and the effect on the results of an electronic nose, experimentation has been performed during more than 3 years on two identical sensor arrays. The two arrays contain the same six Figaro sensors and are in the same sensor chamber of the e-nose system. Both arrays have worked continuously, without break. This paper presents the drift of some TGS sensors for 7 years as well as the difference in the temporal behaviour of identical sensors and the consequence on the e-nose results after the sensor replacement in the sensors array. A correction of the drift and of the replacement effect is applied and the classification results are exposed, with and without correction.