The cell volume increase in individual clones of cells of the yeast Saccharomyces cerevisiae has been measured using time lapse cinematography in populations showing steady state balanced exponential growth. There were significant differences in clonal specific growth rates within the population in each of 10 experiments using different strains on different media supporting different growth rates. The results suggest that specific growth rates of cells which are either genetically identical or very closely related can be different and this difference can be propagated over at least three generations. Since the proliferation rate in yeast is determined by growth rate, these observed differences provide an additional source of cell cycle variability for yeast cells that has not been considered before. The implications for the theoretical analysis of cell cycle kinetics are examined.