Several Nordic research groups are at present conducting research on the properties of NOM. Intercalibration is generally missing and the ongoing research projects do not focus on the physico-chemical properties of NOM. Combining the findings from the research on the physico-chemical properties of NOM is difficult due to large variability in the NOM material. A joint Nordic co-operation on the same set of samples (including RO isolates) will enhance comparability and exchange of understanding about the role of NOM related to the special Nordic conditions. Furthermore, the use of the Nordic Humic standard material in the round Robin intercalibration is of great value in the promotion of this standard and the isolation technique (i.e. RO) chosen.