The specific growth rate (mu) of a respiration-deficient mutant of Saccharomyces cerevisiae growing under defined experimental conditions in batch culture (mineral medium plus glucose and vitamins at 25 degrees C) varied from experiment to experiment over a wide range (0.10-0.24 h-1) and showed a normal distribution. Neither the age of the culture, the history of the inoculum, nor experimental error accounted wholly for the variability of mu. The variation was positively correlated with the specific rate of glucose transfer and negatively with the specific rate of production of non-fermentative CO2. The yield decreased with mu implying higher maintenance requirements in batch culture (4.7 mmoles g-1 h-1) than in continuous culture (0.8 mmoles g-1 h-1). It was concluded that the strain is capable of establishing any one of several steady states of growth under the same experimental conditions, each steady state displaying some build in inertia with respect to change. The variations of the specific rates of glucose transfer and non-fermentative CO2 production, and of the yield appeared to be consequences rather than causes of the variation of mu. The ultimate causes of the variation of mu remained unidentified.