Abstract. Polarized cell division is a fundamental process that occurs in a variety of organisms; it is responsible for the proper positioning of daughter cells and the correct segregation of cytoplasmic components. The SPA2 gene of yeast encodes a nonessential protein that localizes to sites of cell growth and to the site of cytokinesis, spa2 mutants exhibit slightly altered budding patterns. In this report, a genetic screen was used to isolate a novel ochre allele of CDCIO, cdclO-lO; strains containing this mutation require the SPA2 gene for growth. CDCIO encodes a conserved potential GTP-binding protein that previously has been shown to localize to the bud neck and to be important for cytokinesis. The genetic interaction of cdclO-lO and spa2 suggests a role for SPA2 in cytokinesis. Most importantly, strains that contain a cdclO-lO mutation and those containing mutations affecting other putative neck filament proteins do not form buds at their norreal proximal location. The finding that a component involved in cytokinesis is also important in bud site selection provides strong evidence for the cytokinesis tag model; i.e., critical components at the site of cytokinesis are involved in determining the next site of polarized growth and division.