Fouling is still one of the major issues of the membrane bioreactor (MBR) research. Most attention is currently paid to extracellular polymeric substances (EPS) in either bound or soluble/colloidal (soluble microbial products, SMP) form. While several trends or correlations were reported, the comparability of results is still limited by the numerous differences in plant set-up and analytical methods. The aim of this study is to compare polysaccharide concentrations and their respective fouling potentials in different MBRs operated under different conditions using the same analytical and evaluation tools and considering all relevant differences. The results are also compared to the literature findings in an attempt to come to more generally valid conclusions. The results indicate that SMP influence fouling only under certain conditions such as low sludge age and large pore size.