Busulphan [1,4-bis(methanesulfonoxy)butane], an alkylating agent used in the treatment of chronic myelocytic leukemia, was labeled with the positron-emitting radionuclide carbon-11 in a four-step synthetic procedure [1-11C]4-Hydroxybutyronitrile was obtained in 60-70% yield by the reaction of [11C]cyanide with 3-bromopropanol. The nitrile was hydrolysed to [1-11C]gamma-butyrolactone (80-90% yield) with sulfuric acid. Solid phase extraction was used to isolate the lactone and change the solvent before reduction to [1-11C]1,4-butanediol. Dimesylation of the diol with methanesulfonyl chloride in dichloromethane/pyridine yielded [1-11C]busulphan with conversions in the order of 30-35%. The total time of synthesis, including HPLC purification, was 65-75 min from the end-of-trapping of [11C]ammonium cyanide. The decay-corrected isolated yield of no-carrier-added [11C]busulphan was 4-7% and the radiochemical purity was better than 99%.