Hexadecylphospho[methyl-C-14]-choline was synthesized in two steps from the tetra-n-butyl-ammonium salt of phosphoryl[methyl-C-14]-choline and 1-bromohexadecane, and purified by column chromatography on Silica gel. The total yield of the radioactive synthesis was 35%, whereas the total yield of the non-radioactive synthesis was 40%. Hexadecylphospho[methyl-C-14]-choline may serve as a useful tool for pharmacokinetic and biochemical studies of this new antitumor drug.