Immunoanalytical techniques such as ELISA are often used for the detection of proteins produced in cultivation processes. Owing to the difficulty of automating of the time-consuming traditional ELISA, there is an intense demand for a suitable on-line monitoring method. Combining well-known immunoassays with the FIA technique, we present the heterogeneous and the turbidimetric immuno-FIA methods. The following proteins were investigated with these FIA methods: thermostable pullulanase, IgG, antithrombin III, and recombinant tissue-type plasminogen activator. In the cases of pullulanase and monoclonal mouse IgG, the turbidimetric immuno-FIA was used for on-line analysis of the cultivation process. Results are presented here to demonstrate the effectiveness and application of these immunoanalysis.