Branches of Chenopodium album. including leaves and young inflorescences, were put into a solution of 15N-L-proline in order to absorb the latter with the transpiration stream. After 48 hrs of exposure a number of nitrogen fractions were separated. 15N was found in free and bound amino acids, especially in arginine, alanine, glutamic and aspartic acid as well as in amino-lipids and chlorophyll fraction. Proline is considered to be an important source of nitrogen.