The invention relates to a method for isolation of nucleic acids from aqueous samples containing nucleic acids in free form or liberated by lysis. Before or after the polarity of the aqueous solution is lowered, the sample is brought into contact with a solid phase that has a rough or structured surface, whereupon the nucleic acids precipitate on the solid phase and then, together with the solid phase, are removed from this aqueous solution. The rough or structured surface is preferably a non-smooth metal, plastic or rubber surface. Subject matter of the invention is also a test kit and a corresponding instrument for isolation of nucleic acids.