Respiratory rates in two areas of the North Adriatic Sea were studied in the context of a PRISMA II Project, with the aim of quantifying the oxidative processes occurring in the frontal system caused by strong riverine discharge. In the northern area, higher respiratory rates and seasonal variations occurred with respect to the southern area. On average, respiratory activity sustained the oxidation of 66.9 nM C h(-1) inside the front and 24.4 nM C h(-1) outside the front. In conclusion, organic matter oxidation inside the front resulted 2.7 times higher than outside the front. Oxidative metabolism in the Northern Adriatic Sea appears mainly governed by river inputs.