We have offered conventional AEC peroxidase substrate, Cat. No. SK-4200, for many years. While this is our most economical kit format generating 300 ml of working solution, it is also the least sensitive of the three kits. Use of SK-4200 would be for the detection of abundantly expressed antigens and where assay costs are a main consideration. ImmPACT® AEC, Cat. No. SK-4205, was subsequently introduced and offers several advantages over the conventional SK-4200. In particular, SK-4205 is about 3-5 times greater in sensitivity over SK-4200, and the working solution is stable for two weeks when stored at 4°C. ImmPACT® AMEC Red, Cat. No. SK-4285, is our most sensitive AEC substrate that generates a crisper, brighter red reaction product, and is 5-10 times more sensitive when compared with conventional AEC substrates such as SK-4200. Like ImmPACT® AEC, the ImmPACT® AMEC Red working solution can be stored for two weeks in the fridge without loss of staining performance. We have also determined that where archiving of stained sections is important, ImmPACT® AMEC Red remains localized and undiminished in intensity for at least 2 years when coverslipped with VectaMount® AQ Mounting Medium.