In order to perform immunostaining, the tissue specimens should be fixed in appropriate fixative. The purpose of such fixative is to conserve the tissue from autolysis, to preserve tissue structures and to immobilize antigens. However, this requires harsh treatment of the antigens. As a result, antigens undergo chemical alteration of their primary, secondary and tertiary structures. Because of changes in the protein containing epitopes or in neighboring proteins, antigenic sites may be masked. In past, enzymatic treatment with proteolytic enzymes i.e. pepsin, trypsin or pronase has been performed to regain the masked antigens. Shi et al. (1991) have reported that the treatment of the tissue section with heavy metal solution in a microwave can regain the masked antigens significantly. However, heavy metals in the solution increase the risk of exposure to lead for lab personnel. To solve this problem, we have developed a new antigen unmasking solution which is free from heavy metals. Use of this antigen unmasker can prevent the risk of unnecessary exposure for lab personnel and also resolve the handling and disposal problem.