Citrulline is a non-protein amino acid and is produced by the enterocytes of the small bowel. The isolation though ofcitrulline is generally ascribed to the 1930s. In the present article, we demonstrated that before 1930, there was use of the term citrulline, signifying a resin produced by Citrullus Colocynthis. This citrulline is different from modem citrulline. However, neither was modem citrulline isolated in 1930 but somewhat earlier. Reviewing the original manuscripts, Koga and Ohtake (1914) did indeed isolate citrulline for the first time and at least half a dozen other researchers cite their work. Even though their work didn't lead to the determination of the structure and nature of citrulline, theirs was the first to isolate it. Our results have a certain historical and scientific significance and are discussed in extent.