Classical observations on the growth of cells of the fission yeast Schizosaccharomyces pombe indicate that cell length and volume increase to a maximum value, which is reached about three-quarters of the way through the growth cycle, followed by a constant volume plateau. The authors have reexamined the growth of these cells by phase microscopy. When growth conditions were perturbed by inoculating cells at high density, in the presence of contaminant, or upon agar slips containing the growth medium in 4% agar, all cells grew in the classical pattern. But, at smaller agar concentrations and lower cell densities, many cells grew at a constant rate throughout the entire cell cycle. Also, the frequency of this linear pattern of cell growth increased as growth perturbations were reduced. They interpret these results as evidence for a sensitivity of this microorganism to perturbations of steady-state growth. The constant rate of volume increase throughout the cell cycle in unperturbed cells, when considered along with Mitchison's earlier results for constant dry mass increase, suggests that the buoyant densities of these cells remain constant during the entire cell cycle.