The isolation of L(+)-methionine sulphoxide from the blowfly Phormia regina Meigen.

1. l(+)-Methionine sulphoxide has been isolated for the first time from a natural source, the blowfly Phormia regina. 2. The natural compound is shown to be identical with the synthetic by a number of criteria, including optical rotatory dispersion and infrared spectrum. 3. The methionine sulphoxide occurs in only a small concentration in the late larval and early pupal stages of the blowfly, but the titre increases rapidly in the later pupal stage and remains at a high level during the adult stage.