The proteins from cytoplasmic ribosomal subunits of eight species of algae were analyzed by two-dimensional gel electrophoresis. The molecular weights of the proteins were in the range of 10,000 to 55,000. We have compared the protein patterns from the ribosomal subunits of the different species to those of Chlamydomonas reinhardii. It was quite clear that there are many similarities in the protein patterns of all the investigated species. We found for Chlamydomonas eugametos 48, Chlamydomonas noctigama 42, Chlorogonium elongatum 47, Scenedesmus obliquus 40, Chlorella fusca 35, and Euglena gracilis 35 proteins which were homologous to those of Chlamydomonas reinhardii. For the colorless flagellate Polytoma papillatum, we detected 45 proteins homologous to Chlamydomonas reinhardii, so that the generally assumed close relationship between Chlamydomonas and Polytoma is confirmed.