Retention of fines and additives by retention aids is important for pulp yield and paper quality in the pulp and paper industry. Measurement of the adsorption of various proteins on different cellulosic substrates was used to evaluate their potential as retention aids. Commercially obtained proteins and bacterial proteins extracted from aBacillus subtilisstrain showed substantial adsorption on three of the five cellulosic substrates tested. Proteins with high pI values were better adsorbed on cellulosic substrates.