Bovine serum albumin (BSA) is used extensively as a carrier protein to dilute antibodies and as a general protein blocking agent in immunoassays and immunodetection protocols. Unfortunately, many commercial preparations of BSA, even some of the highest purity grades, contain IgG that may become an antigen for cross-reacting secondary antibodies. This is particularly common when using anti-bovine IgG, anti-goat IgG (with the exception of bovine anti-goat IgG), rabbit anti-horse IgG, or anti-sheep IgG, but may occur with other antibodies that cross-react with bovine IgG. The result of these interactions may be loss of desired antibody activity, loss of antibody stability, and/or increased background. Background may derive from sticky soluble immune complexes or from contaminating bovine IgG sticking non-specifically and attracting cross-reacting labeled secondary antibodies. Even small amounts of contaminating IgG may create these problems, due to the use of high concentrations of BSA in many protocols. Our IgG-free BSA, which is also protease-free, alleviates many of these problems. IgG-free BSA is supplied as a pure protein, freeze-dried from deionized water.