On the late nineties, recurrent episodes of odor nuisance were produced on the Besos river basic with special incidence on the nearby city of Montecada i Reixac, particularly during the dry summer season. In order to gain more information about the phenomenon, an appropriate H2S emission survey program was designed, by means of two monitorization stations, one fixed and another mobile, equipped with continuous real-time analyzers. The H2S was analyzed by previous oxidation to SO2, followed by molecular fluorescence determination of this compound. During the 1994 summer period the measured levels of H2S concentration, meteorologic conditions and occurrence of odor episodes was evident.