Protein labeling kits ProtOn Biotin and ProtOn Fluorescein label antibodies, hormones and other proteins quickly and easily. The biotin or fluorescein labeled proteins have stable linkages and are ideal for immunological assays, immunochemical or fluorescence microscopy, or related applications. These kits contain sufficient labeling reagent, solvent, buffer, stop reagent, gel filtration slurry, spin columns and collections tubes to perform 5 labelings of up to 1 mg protein each. The ProtOn Biotin Labeling Kit also contains agarose avidin for measuring the degree of biotinylation. Kits are convenient and accompanied by easy-to-follow instructions.