By immunochemical methods we had presented evidence for a primary acceptor complex for photosystem I of photosynthetic electron transport. During purification of this complex, obtained as a water soluble fraction from ether treated lyophilized chloroplasts, two low molecular fractions are also obtained, which may or may not have relation to the primary acceptor. The purification and identification of these low molecular fractions is reported. One, absorbing at 275 and 335 nm, consists of several flavonoid glycosides. The aglycon of the main component is tentatively identified as a 3-methyl-6,7-methylenedioxy-quercetagetin. The chromophore of the other low molecular fraction, absorbing at 312 nm, contains two cinnamic acid derivatives, which on alkaline hydrolysis yield p-coumaric acid. The relation of the two low molecular fractions to other fractions of various activity isolated from chloroplasts is discussed.