The substrate kits offered for use with the glucose oxidase system provide maximum sensitivity and optimal staining for glucose oxidase. The glucose oxidase substrate kits are based on the oxidation of glucose and the reduction of tetrazolium salts to colored, insoluble formazans. Each kit contains stock solutions in convenient dropper bottles, a mixing bottle to prepare working solutions, and clear, detailed instructions for use. Each kit is designed to provide approximately 300 ml of working substrate solution which is usually sufficient to stain 1000-3000 tissue sections, and is stable for one year when stored at 4 ÂșC.