The growth response of Saccharomyces cerevisiae to magnesium limitation when propagated aerobically in batch culture under conditions of glucose repression was hyperbolic, thus indicating a Monod relationship The saturation coefficient, K-s, was 36 mu M magnesium, and exogenous magnesium requirements for optimal yeast growth rate were established in minimal medium. An investigation into growth and metabolism of S. cerevisiae over a range of growth rates using a magnesium-limited chemostat revealed that at growth rates less than mu(max), cells exhibited a physiological state characteristic of non-carbon-limited growth. This was exemplified by an increase in the biomass yield from increased magnesium availability and alterations in the relative contributions of fermentation and respiration to the overall respirofermentative activity as the growth rate increased reward mu(max). Studies on the growth behaviour of S. cerevisiae when cells were released from magnesium limitation within a chemostat suggested that magnesium primarily exerts its influence on cell division cycle progression in this yeast.