Method for isolating nucleic acids

A method for isolating or purifying short-chain nucleic acids that are ≦500 bp from a short-chain nucleic acid-containing starting material, comprising:

• (a) binding the short-chain nucleic acids to a nucleic acid-binding support material by contacting the starting material with said nucleic acid-binding support material in the presence of at least one chaotropic compound and at least one branched or unbranched alcohol, wherein
• the at least one branched or unbranched alcohol is isopropanol and is present at a concentration of at least 15% (v/v) and at most 25% (v/v),
• a non-ionic detergent is present during binding,
• the nucleic acid-binding support material is selected from the group consisting of siliceous materials, silica gel, silicon dioxide, glass, zeolite, kaolin, gelatinous silica, ceramics, silica membrane, and magnetic particles having a silica or glass surface,
• the concentration of the chaotropic compound in step a) is ≧2 mol/l,
• the short-chain nucleic acids are extracellular DNA, and
• the short-chain nucleic acid-containing starting material is plasma or serum.