1. A previously unidentified compound first observed in the serum of children with kwashiorkor has been isolated from the urine of experimental protein malnourished rats.
2. On mass spectroscopy and nuclear-magnetic-resonance spectroscopy the unknown compound appeared identical with authentic piperidine-2-carboxylic acid. This identity was confirmed by the behaviour of the unknown and authentic compounds on paper, ion-exchange, thin-layer or gas-liquid chromatography.
3. The significance of the accumulation of piperidine-2-carboxylic acid in the serum of children with kwashiorkor is discussed.