Unstructured models for cell growth (cell specific growth and death rate) and metabolism (cell specific substrate uptake and metabolite production rates) of hybridoma cell lines were compared with special respect to significance, analytical error and range of validity. The diversity of the unstructured models cited reveals their mostly descriptive character compared to structured models. Bearing in mind this limited knowledge, empirical models can still serve as a valuable tool for process design. For understanding of the cell metabolism itself they might have been overemphasized in the past. For proper model design, care has to be taken to cover the whole range of process conditions. In particular, if a process is to be run at very low substrate and high metabolite concentrations, chemostat cultures which have mostly been used for the model formulations, are not sufficient and have to be completed by, for example, fed-batch cultures.
