Supercomplex organization of photosystem complexes was studied in various cyanobacteria, a glaucocystophyte and a primitive rhodophyte by blue-native PAGE. As already shown in Thermosynechococcus elongatus, PSII complexes yielded the dimeric and monomeric forms. In any case, the recovery of the dimeric PSII was increased at high detergent concentrations. On the other hand, there were unexpected variations in the organization of the PSI supercomplexes depending on the species. In filamentous N2-fixing cyanobacterium Anabaena sp. PCC 7120 and a glaucocystophyte Cyanophora paradoxa gave PSI tetramer and dimer but no trimer at all.