Abstract: Sensitive proteins in human biological secretion samples are preserved by dispersing them in an aqueous solution containing from 0.05 to 0.5M of a buffer which is effective to maintain the solution pH within the range of from 6.5 to 8.0; from 0.1 to 10 wt. % of a non-immune animal protein selected from the group consisting of albumin, ovalbumin, casein, glycoprotein and mixtures thereof; from 40 to 2000 kallikrein units/mL of an enzyme inhibitor of trypsin, chymotrypsin, kallikrein or plasmin; and from 0.01 to 0.1 wt. % of a bacteriostatic agent. The solution preferably also contains from 5 .mu.M to 1 mM of a protease inhibitor; and from 1 to 10 mM of a chelating agent. Optimally, the enzyme inhibitor is aprotinin, the protease inhibitor is phenylmethylsulfonylfluoride, the non-immune animal protein is bovine serum albumin, and the protease inhibitor is phenylmethylsulfonylfluoride. 0.0 to 0.15 mM of a water-soluble non-interfering salt, such as NaCl, may be desired.