This study provides an insight on whether a systematic inclusion of releases and transfers from small and medium-sized enterprises (SMEs) in national Pollutant Release and Transfer Registers (PRTRs) would improve the current knowledge of industrial pollution as a whole. The study concludes that in order to be able to cover the remaining releases and transfers from SMEs, diffuse sources should be included in PRTRs.(Original source: http://www.oecd.org/dataoecd/18/20/40596852.pdf)