[en] The method is described of producing ¹⁴C-labelled 2,3-dihydroxypropyl derivatives of adenine and thymine of the general formula CH₂OH-CHOH-CH₂B, where B is adenine-9-yl, thymine-1-yl or thymine-3-yl residue labelled with ¹⁴C. ¹⁴C-labelled adenine or thymine is evaporated with 2 to 3 equivalents of an aqueous or aqueous-alcoholic solution of sodium or potassium hydroxnde and after drying it is reacted with 1 to 3 equivalents of (S)-, (R)- or (RS)-1-O-p-toluenesulfonyl-2,3-O-isopropylideneglycerine in water-free dimethyl formamide as a solvent at a temperature of 80 to 130 degC, to advantage at 110 degC. After solvent evaporation and evaporate heating in an acid medium, to advantage in 80% acetic acid, at a temperature of 50 to 100 degC, the product is separated by paper chromatography. (B.S.)