A collection container and a method for collecting a biological sample, particularly whole blood, includes at least one stabilizing agent in an amount effective to stabilize and inhibit protein degradation and/or fragmentation. The stabilizing agent is able to stabilize proteases in the biological sample, particularly at the point of collection, by inhibiting protein degradation and/or fragmentation in the sample when the sample is stored. The stabilizing agent comprises or consists of one or more protease inhibitors.