Streptoverticillum sp. transglutaminase was used as catalyst for the attachment of several beta-cyclodextrin derivatives to the glutamine residues in bovine pancreatic trypsin. The modifying agents used were mono-6-ethylenediamino-6-deoxy-beta-cyclodextrin, mono-6-propylenediamino-6-deoxy-beta-cyclodextrin, mono-6-butylenediamino-6-deoxy-beta-cyclodextrin and mono-6-hexylenediamino-6-deoxy-beta-cyclodextrin. The transformed trypsin preparations contained about 3 mol of oligosaccharides/mol of protein. The specific esterolytic activity of trypsin was increased by about 4-21% after conjugation. The K (m) values for cyclodextrin-trypsin complexes represented about 58-87% of that corresponding to the native enzyme. The optimum temperature for esterolytic activity of trypsin was increased by about 5-10 degrees C after enzymic modification with the cyclodextrin derivatives. The thermostability was increased by 16 degrees C for the modified trypsin. Thermal inactivation at different temperatures ranging from 45 to 60 degrees C was markedly increased for the oligosaccharide-trypsin complexes. This modification also protected the enzyme against autolysis at alkaline pH.