Fundamental aspects of chemostat cultures are reviewed. Using yeast cultures as examples, it is shown that steady states in chemostats may be predicted quant. by combining the correct no. of unstructured kinetic models with expressions for existing stoichiometric constraints. The necessary no. of such kinetic models corresponds to the no. of limiting substrates and increases with the no. of different metabolic pathways available to the strain. This is demonstrated by an exptl. comparison of yeast growth limited by glucose alone for which metab. is oxidative, and growth doubly limited by both glucose and oxygen, which occurs according to an oxido-reductive metab. The steady state data for such expts. can in principle be predicted based on a minimal amt. of information by a simple stoichiometric model. It represents the overall stoichiometry of growth by a superposition of a fully oxidative and a fully reductive growth reaction and uses the concept of \"aerobicity\" to characterize the relative importance of the two reactions. [on SciFinder (R)]