Resonance Raman spectroscopy of an antenna protein from the brown alga Laminaria saccharina has been used to investigate the molecular structure of this light-harvesting complex (LHC) at the level of its bound pigments, chlorophylls (chl) a and c and the xanthophyll fucoxanthin. Evidence has been obtained for the conservation of pigment structure during the isolation procedure used. Six chl a and two chl c molecules are indicated from the positions and relative contributions of stretching modes of their keto-carbonyl groups. Of special interest is the presence of a population of chls a having a protein-binding conformation highly similar to that seen in antenna proteins from higher plants, possibly indicating a common structural motif within this extended gene family. The eight fucoxanthin molecules evidenced are all in the all-trans conformation; however, one or two have a highly twisted configuration. The results are discussed in terms of common and varying structural features of LHCs in higher plants and algae.