Size exclusion chromatography (SEC) is an effective way to refold denatured proteins. However, due to the contact between the refolding buffer (mobile phase) and the injected denatured protein (sample), immediate aggregation from injector and column inlet was found to be a barrier of effective refolding. A chaperon solvent plug strategy was, therefore, developed to overcome this problem. That is, the denatured protein was escorted from the injector into the column by a solvent plug that could inhibit formation of aggregates. The refolding of denatured lysozyme in SEC by this method was experimentally shown to reduce the aggregation and, thus, to enhance both mass and activity recoveries simultaneously. (C) 2003 Elsevier Inc. All rights reserved.