Spectroscopic monitoring techniques have many advantages for bioprocess monitoring and control, including simultaneous multi-analyte detns., in-situ sterilizability, and low maintenance during operation. This study discusses the combined application of fluorescence, mid-IR, and Raman spectroscopic techniques for a comprehensive monitoring of Phaffia rhodozyma yeast cultures during batch and fed-batch operation for the prodn. of astaxanthin, a carotenoid of industrial importance. Reliability of the different techniques will be detailed along with their utility to control the growth rate at an optimum value. [on SciFinder (R)]