We report on single-molecule experiments that were performed on two biological systems, the recently cloned red fluorescent protein of a coral of the Discosoma genus (DsRed) and the enhanced green fluorescent protein, both of which were immobilized in polyvinylalcohol. Fluorescence intensity trajectories were recorded and compared to those of a reference compound, the organic dye hexaphenylbenzene perylenemonoimide. Evidence was found for the presence of DsRed as an oligomer even at subnanomolar concentrations. Both proteins show triplet blinking in the millisecond time range. Collective effects could be observed for the Dsred oligomers.