Special Serum Diluting Buffer is PBS-0.09% sodium azide with 10% adult bovine serum added. Adult bovine serum is used in this diluting buffer instead of BSA because some vaccines used in canine, feline and porcine species contain bovine serum components which cause antibodies to be made that may give a high background fluorescence on IFA. Adding bovine serum to the diluent increases the globulin fraction sufficiently to block any antibody that might react with residual bovine globulin on the cells on the substrate slide, and thus reduce the background fluorescence. Formerly catalog number 210-94-SB