HPLC analysis of a hydrolyzed extract obtained from the aerial parts of CHELIDONIUM MAJUS yielded 0.4% caffeic, 0.06% P-coumaric, and 0.02% ferulic acids; gentisic and P-hydroxybenzoic acids were below 0.01%. The caffeic acid derivatives occur as esters of which four were isolated using gel permeation chromatography, centrifugal partition chromatography and HPLC; they were assigned on the basis of their spectroscopic data ( (1)H-, (13)C-NMR, UV, MS) as the new (-)-2-( E)-caffeoyl- D-glyceric acid, (-)-4-( E)-caffeoyl- L-threonic acid, (-)-2-( E)-caffeoyl- L-threonic acid lactone, and the known (+)-( E)-caffeoyl- L-malic acid.