The invention relates to a method and kits for isolating and/or purifying nucleic acids, in particular, short-chain nucleic acids, from a nucleic acid containing starting material, characterised by the following method steps: (a) bonding the nucleic acids to a nucleic acid bonding support material, wherein the starting material is brought into contact with the nucleic acid bonding support material in the presence of at least one chaotropic compound and preferably isopropanol, wherein the isopropanol is present in a concentration of ≧15% (v/v) and ≦35% (v/v), (b) optional elution of the bonded nucleic acids from the nucleic acid bonding support material. Said method is particularly suitable for the purification of foetal DNA from maternal blood