London Resin (LR) White a hydrophilic embedding medium for immunocytochemistry, can be polymerized in a commercial microwave oven in seven minutes using the chemical accelerator benzoyl peroxide. In order to minimize the effects of heating, the polymerization vessel was maintained in an ice bath. We demonstrate that this procedure does not affect the antigenicity of either barley aleurone nuclease or of the catalytic and regulatory subunits of rat parotid cAMP-dependent protein kinase.