Comprehensive and cGMP suitable bioprocess monitoring is still a challenge in microbial fermn. and cell culture process development. This paper discusses the exploitation of in-situ mid-IR spectroscopy in combination with partial least-squares anal. to monitor carbohydrate, amino acid, org. acid, pH, temp., and biomass content of Saccharomyces Cerevisiae, Phaffia rhodozyma, and CHO cell cultures. Reliability of the monitored values will be discussed for potential application in cGMP environments along with case studies to increase the productivity by using the information for controlling the processes. [on SciFinder (R)]