Shi et al. (1991) have reported that treating tissue sections with a heavy metal solution in a microwave oven can cover masked antigens significantly. However, heavy metals in the solution increase the risk of toxic exposure to lab personnel. To reduce the risk, we have developed an antigen unmasking solution which is free of heavy metals. The reagent is provided in a convenient 10X concentrate. Use of this antigen recovery buffer avoids unnecessary heavy metal exposure to lab personal and handling and disposal issues.