Six different globular proteins were filtered with hydrophilic regenerated cellulose ultrafiltration membranes at their isoelectric points. The PLS regression was used to analyse the filtration data. The modelling of the relative flux failed, but that of the transmission of the proteins succeeded relatively well. As a conclusion of the data analysis the most important explanatory variables affecting the transmission of proteins are the permeate flux and the membrane cut-off value divided by the molar mass of the protein. They both have a positive linear relationship with the transmission.