An automated immunoassay, with one affinity component immobilized on a solid surface, has been developed to monitor the production of different immunoglobulins during mammalian cell cultivation processes. The whole analysis device is based on the principle of flow injection analysis (FIA) and a cartridge with the immobilized affinity component is implemented into the FIA system. This cartridge is filled with a carrier material to which protein G is covalently bound. After sample injection, binding of the IgG on the protein G within the cartridge takes place while after a washing step, the IgGs are eluted by a pH shift, and the IgG concentration is monitored via fluorescence. In the automated immunoassay, undiluted cell free samples from the reactor or from down-stream processing can be analyzed directly. Due to the separation the IgG can be detected without interference from other sample components by protein fluorescence. The results are obtained with analysis times below 6 min. Sample volumes of less than 100 microliters may be used. The assay is sensitive to concentrations from 5 up to 500 micrograms ml-1. Using this FIA-System, immunoglobulins G, produced in different media, were successfully monitored. The results of the assay were validated by ELISA.