Ultrafiltration of goat pancreatic extract to obtain trypsin, using Soybean Trypsin Inhibitor as affinity ligand and a 30 kDa MWCO polyethersulfone membrane, is studied by examining the effect of varying transmembrane pressure and pancreatic extract: wash buffer ratio on active trypsin yield and flux/throughput profiles. For all process conditions considered, no detectable trypsin activity is found in the washing-phase permeates confirming excellent ligand-trypsin binding. Maximum trypsin yield obtained, at 1:1 feed ratio and 4 kg/cm(2) pressure, is 74%. Mass flux of eluted protein as well as of washed-off impurities are also maximized under these conditions.