A review with 29 refs. of lab.-scale investigations carried out on the usefulness of biol. heat-release measurements, as a means for monitoring and controlling the metabolic state of microbial cultures. Such studies are carried out in high-quality bench-scale calorimeters, but measuring heat generation rates by establishing energy balances ought to be applicable to large-scale bioreactors without resorting to sophisticated instrumentation. The signal received can either be interpreted by more qual. correlation with the evolution of the culture, or it may be quant. exploited -together with other online measurements - in order to assess the rates at which various types of metabs. proceed in the culture. The work described shows how this can be used to keep a culture in a desired metabolic state during fed-batch and transient continuous cultures of the yeast, S. cerevisae, and how a bacterial fed-batch culture can be controlled in order to optimize biosynthesis of an antibiotic. [on SciFinder (R)]