A method for purifying a protected oligonucleotide comprising the steps of: a) providing a solution of the protected oligonucleotide in at least one solvent A having a boiling point below the boiling point of a solvent B, heating the solution at a temperature of at least 30.degree. C. and below the boiling point of the at least solvent A, adding solvent B until precipitation of a material is visible in the solution, said solvent B being an alcohol having 1 to 6 C-atoms or a diol having 2 to 6 C-atoms, allowing the solution to cool down under stirring until formation of a supernatant and a residue, removing the supernatantor b) providing solvent B, said solvent B being an alcohol having 1 to 6 C-atoms or a diol having 2 to 6 C-atoms, heating solvent B at a temperature above 30.degree. C. and below the boiling point of solvent B, adding a solution of a protected oligonucleotide in at least one solvent A until precipitation of a material is visible in the solution, allowing the solution to cool down under stirring until formation of a supernatant and a residue, removing the supernatant.