THE division of a yeast cell by budding gives rise to two cells which are identifiable, that is, the mother cell from which the bud arose, and the daughter cell which developed from the bud. The wall of the daughter cell presumably is synthesized de novo while that of the mother cell retains all or at least part of its identity through the division-an example of linear inheritance1. That the wall of the mother cell is not reformed is evidenced by the accumulation of scars associated with each budding event2. Electron micrographs3-5 reveal a scar area that is approximately 1 per cent of the surface area of the cells. If, as indicated by Barton2, a bud is never formed at the site of a scar, then it is possible that the life-span of individual cells would be limited by depletion of available budding sites. Barton observed one cell to bud 23 times but did not observe a cessation of budding. Other progressive changes also might limit the number of divisions that a single cell can complete. This report describes an experiment designed to determine the life-span of single yeast cells and includes consideration of possible mechanisms for life-span limitation.