HIS minireview discusses recent information about the septin family of proteins, which suggests that the septins may be elements of a new filament system that functions in all or most eukaryotic cells. Septins are found in a wide variety of eukaryotes, are important for cytokinesis, and may compose or regulate a ubiquitous fil- ament system that has not been previously recognized. A more extensive review of septins was recently published (26). This minireview also presents a new comparison of septin sequences. Actin filaments, microtubules, intermediate filaments, and myosin thick filaments, have been extensively studied over the past several decades, using methodologic ad- vances in electron and light microscopy, detergent extrac- tion of cells, and purification of proteins. This collection of filaments has been assumed to represent a fairly complete picture of the cytoskeletal filaments commonly found in eukaryotes. However, recent work suggests that cells aug- ment these common cytoskeletal elements with additional elements, at least one of which, the septins, appears to be widely expressed and used for essential cell processes.