The present invention is directed to a method for adsorbing, i.e. non-covalently binding, nucleic acids to a solid phase using a two-step procedure. Furthermore, the present invention pertains to a method for isolating nucleic acids from a biological sample. In the first step of the procedure, lysis is effected by mixing the biological sample with an aqueous lysis buffer containing a chaotropic agent and incubating the mixture; in the second step, the concentration of the chaotropic agent in the mixture is increased and the mixture is contacted with the solid phase, whereby the nucleic acids in the liquid phase is adsorbed to the solid phase.