The authors have previously reported a new fixation and paraffin-embedding method (the AMeX method), which preserves many antigens as well as high molecular-weight DNA and RNA that are normally destroyed by the routine formalin fixation and paraffin-embedding process. In the present study, the authors analyzed the preservation of protein suitable for sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting in tissue fixed by the AMeX method. The method used for extraction of protein from AMeX-processed tissue sections after deparaffinization was the same as that for extraction from fresh tissues. The total amount of protein extracted from 50-mg (wet weight) AMeX-processed mouse liver tissue was the same as that from fresh tissue. The electrophoretic mobility and staining intensity of protein on SDS-polyacrylamide gel, and the immunoblotting pattern and staining intensity with several antibodies, were identical for both AMeX-processed and fresh tissue. Degradation of protein was minimal for storage periods of 2 years in paraffin block. The authors also showed that pellets of cultured cells can be processed by this method for immunologic analysis. This new fixation and paraffin-embedding method is a useful tool for obtaining information on correlations between morphologic features and immunochemical and molecular biological data.