Abstract: A procedure for preparing L-(methyl-3H)-methionine is described. The method involves the tritiated sodium borohydride reduction of formaldehyde. This will be followed by io-dation to give a 80% yield of tritiated methyl iodide. Direct alkylation of the L-homo-cysteine anion, generated by the sodium-liquid ammonia reduction of L-methionine, by methyl-T iodide gives L-(methyl-3H)-methionine with 27% yield after purification. The specific activity of labelled methionine is 12.5 Ci/mM. The radiochemical purity is over 95%.Mass spectrum and NMR spectroscopy of deuterated methionine, prepared from deu-terated methyl iodide by the same method, show that the deuterium content of the S-methyl group is the same as that of the methyl iodide, and methionine specifically labelled in the methyl group is obtained.