To meet the requirements of the Baltic Sea Declaration which insist on a 50 percent reduction in the discharge of potential hazardous pollutants (organics) to the Baltic Sea by 1995, it is necessary to provide reliable assessments of the pollution loads received by rivers entering the Baltic. In this paper the estimation of input loads via rivers is discussed, with particular reference to monitoring requirements and analytical performance criteria. The author makes use of the data sets obtained in a three-year study on the concentrations of biocides in Polish rivers. Considering the monitoring requirements and taking into account the accuracy of the routine analytical methods which are in use now in Poland, it becomes obvious that there is an urgent need of substituting them with analytical methods of higher accuracy.