The present invention provides a method of substantially retaining or otherwise preserving the biological activity of a dsRNA, present in a cell lysate, to post-transcriptionally silence the expression of a gene in a target organism, comprising the step of adding to the lysate a compound having the function of a protein- or amine-cross linking agent. The invention also comprises compositions comprising the lysate comprising dsRNA, and protein cross linking agents, as well as the use of said agents in the method.
