sebum in naturally soiled cotton undershirt and oleic acid in artificially soiled cotton cloth, which entered interfiber space in the interior of cotton fibers were easily removed by alkaline cellulase from bacillus sp., but only with difficulty by commonly used detergent ingredients such as surfactant and protease adsorption isotherms and the rate of hydrolysis of alkaline cellulase against insoluble cellulose powders revealed that the lower the relative crystallinity of cellulose powder, the more adsorptive alkaline cellulase became and the more hydrolysis was promoted. with alkaline cellulase, cotton having the highest relative crystallinity was adsorbed at ph 9 and 5 $degree$ c, liberated a negligible small amount of reducing sugar at ph 9 and 40 $degree$ c, and produced no changes in the degree of polymerization of cotton cellulose and in the tensile strength of cotton fabric at ph 9 and 30 $degree$ c. on the other hand, differential scanning calorimetric studies revealed that under similar conditions even a small quantity of alkaline cellulase drastically reduced the amount of water bound to cellulose in cotton. because water was bound only with hydroxy groups of cellulose molecules in the amorphous region of cotton fibers, it can be understood that soil entering the interfiber space of amorphous interlamellae in the interior of cotton fibers, was easily removed as the hydrated cellulose in the interlamellae was slightly hydrolyzed by alkaline cellulase. a new detergent mechanism is proposed. (author abstract) 17 refs