Microwave irradiation of tissue sections in a solution containing lead salt has been reported to enhance immunohistochemical staining of formalin-fixed, paraffin-embedded materials. To compare the effectiveness of this procedure with protease digestion, which is widely used for the same purpose, we tested 50 pairs of tissue samples, one group fixed overnight and the other intentionally overfixed for 5 days in 10% formalin. The tissue sections were stained with 17 diagnostically useful monoclonal and polyclonal antibodies using the avidin-biotin immunohistochemical method as follows: (a) no special treatment, (b) digestion with 0.1% pronase for 5 min, (c) digestion with 0.1% trypsin for 10 min, and (d) microwave irradiation of sections in the commercially available lead thiocyanate solution as recommended by the manufacturer. Both pronase and trypsin treatment showed improvement of staining of five of the antibodies used. The microwave/metal solution procedure improved the staining with two antibodies (vimentin and glial fibrillary acidic protein), worsened the staining of another four antibodies, and did not modify the remainder. However, staining for glial fibrillary acidic protein was similarly improved by protease digestion. Our results fail to confirm the reported superiority of antigen retrieval by microwave heating in lead salt solutions over protease digestion. Moreover, the microwave/lead salt method has the added disadvantage that it increases laboratory hazards and requires special equipment.