This studywas designed to yield data on the supramolecular organization of the phycobilisome apparatus from Synechocystis, and the possible effects of environmental stress on this arrangement. Phycobilisomes were dissociated ina low ionic strength solutionandaquantitative estimation of the protein components present in each subcomplex was obtained using liquid chromatography coupled on-line with a mass spectrometer equipped with an electrospray ion source (ESI-MS).