The adsorption characteristics of insulinotropin, a 31-amino acid peptide, to several different sterilizing filters were investigated in the present report. The 0.2 micron filters used in the study were a Nylon-66 filter, a hydroxyl-modified polyamide (BioInert) filter, a polyvinylidene fluoride (PVDF) filter, and a polyhydroxy-propyl-acrylate-grafted polyvinylidene fluoride (GV) filter. The results indicate a rank ordering of adsorption (low to high) of GV, BioInert, Nylon-66, and PVDF. Based on these results, it is possible to predict the amount of solution which must be passed through the specific filter to saturate the binding sites per unit area.