Alternative hosts for expressing heterologous proteins have recently gained an increased attention. Actinomycetes, and among these especially the Streptomycetes are considered promising candidates, since they through their saprophytic lifestyle are capable of excreting large amounts of proteins. Industrially this is very useful due to the reduction of downstream processing. Streptomycetes have long been studied, and a great amount of knowledge has been gained on genetic tools and metabolism. A most promising candidate as host among the Streptomycetes is S. lividans, since this strain exhibits an exceptionally low protease activity, ensuring good product stability. Despite the fact that S. lividans has already seen industrial application studies on quantitative physiology are still lacking. It will greatly benefit the use as a common host to elucidate how S. lividans behaves in submerged cultivations, as well as how it is affected by expressing a foreign protein. In this thesis methods have been established for the study of quantitative physiology and a method for screening large amounts of carbon/nitrogen/phosphorus sources have been tested. Further, parallel to the project that is the basis of the thesis is an EU project that has had to be supported with physiological data. Cultivations have been run across laboratory relevant scales. A strong physiology platform is required to obtain the most informative results from the advanced ‘omics’ analyses. Whether the biomass is harvested from batch or chemostat experiments, reproducibility is essential for comparing results under controlled conditions.