Blocking Buffer I is based on a low-molecular weight, highly purified casein with NaCl and Tween® and stabilised with 0,1% ProClin® 300. It does not contain glycosylated proteins. Blocking Buffer I saturates free binding capacities on plastic consumables and other surfaces like ELISA plates and blotting membranes. Thus a reduction of unspecific binding on surfaces can be achieved. Efficiency of blocking is significantly improved in comparison to standard blocking procedures by a special production method, which leads to casein molecules with many different molecular sizes. Blocking Buffer I can be used in ELISA, EIA, RIA, Western blotting, immuno-PCR, protein arrays as well as immunohistochemistry.