At -70 degree C. Avoid repeated freezing and thawing. It is recommended to aliquot the product after the first thawing. To prepare diluted samples of proBNP it is recommended to use buffer solutions containing carrier protein and detergent (e.g. 0.05 M Tris-HCl, pH 7.8, 0.15 M NaCl, 0.01 % Tween 40, 0.5 % bovine serum albumin).