In this paper, two different FIA-based biosensor systems are described for application to different biotechnologically relevant purposes. In the first system, single fiber optodes were used to determine the pH, urea and penicillin V concentrations. A two-channel system was developed for the simultaneous monitoring of different variables to increase the analysis accuracy. This system was used for monitoring the penicillin V concentration during a cultivation of Penicillium chrysogenum. The second system described is a calorimetric immunoassay based on the use of an enzyme thermistor. A sandwich assay with protein A immobilized on a solid support for the determination of various IgGs was established. A fusion protein of protein A and beta-galactosidase obtained from a recombinant E. coli strain was used in the labelling and detection reaction. This system is designed for future application in bioprocess monitoring.