alpha-Chymotrypsin was lyophilized in the presence of 2,3,6-tri-O-methyl beta-cyclodextrin, and it displayed activity 40 fold higher than free alpha-chymotrypsin for transesterification in acetonitrile. alpha-Chymotrypsin which was co-lyophilized with hydroxypropylated beta- or gamma-cyclodextrins retained more than 98% of its initial activity after 6 h incubation in acetonitrile.