Hen egg white lysozyme was immobilized by carboniimide method to form amide bonds with a polymer (AS-L) showing reversibly soluble-insoluble characteristics with pH change. The immobilized enzyme (LY-AS) was soluble above pH 6 and precipitate below pH 4.5, offering advantages in that it can carry our hydrolysis of microbial cells in a soluble form yet be recovered after precipitation at low pH. The maximum specific activity of LY-AS was 66% of that of free lysozyme with M. lysodeikticus cells as substrate, which is much higher than the values reported in the literature using water-insoluble materials as carriers. The effects of pH and temperature on the activity of LY-AS were studied and compared with those of free lysozyme. With repeated pH cycles between 6.6 and 4.5, the operation half-life of immobilized enzyme activity was nine cycles. Repeated batch lysis of microbial cells could be carried out with intermittent enzyme precipitation and recovery steps. In such an operation the insoluble residual cells should be recovered together with the immobilized enzyme to minimize enzyme loss arising from adsorption to cells. (C) 1997 Elsevier Science Ltd.