The 4-CN peroxidase substrate kit produces an insoluble blue/gray reaction product and can be used for development of nitrocellulose blots. This substrate is not recommended for immunohistochemical applications. The reagents in this peroxidase substrate kit are supplied as concentrated stock solutions in convenient dropper bottles. The kit provides all of the necessary reagents to prepare about 300 ml of working solution. When stored at 4 ºC, this kit is stable for one year.