Abstract: A synthesis of and use for L-Se-methylselenocysteine as a nutriceutical is described, based upon the knowledge that L-Se-methylselenocysteine is less toxic than L-selenomethionine towards normal cells. The synthesis proceeds by mixing N-(tert-butoxycarbonyl)-L-serine with a dialkyl diazodicarboxylate and at least one of a trialkylphosphine, triarylphosphine, and phosphite to form a first mixture that includes N-(tert-butoxycarbonyl)-L-serine &bgr;-lactone. Methyl selenol or its salt is mixed with the N-(tert-butoxycarbonyl)-L-serine &bgr;-lactone to form a second mixture that includes N-(tert-butoxycarbonyl)-Se-methylselenocysteine. The tert-butoxycarbonyl group is removed from the N-(tert-butoxycarbonyl)-Se-methylselenocysteine to form L-Se-methylselenocysteine. This synthesis significantly improves the manufacturability, manufacturing efficiency, and utility of this naturally occurring rare form of organic-selenium.