Chitin synthesis occurs in most fungi through the action of different chitin synthase (CS) isoenzymes. In Schizosaccharomyces pombe the chs2(+) gene codes for a protein with significant similarity to CS enzymes, but lacking most of the residues considered to be essential for activity, including the QRRRW domain. Here we show that chs2p is a functional protein that localises to the growing edge of the septum but is not a CS enzyme. Strong over-expression is lethal, while moderate expression leads to a severe defect in septum formation. These results suggest that chs2p has remained through evolution to play an alternative role in septation.