Mid-IR (MIR) spectroscopy in combination with partial least-squares (PLS) regression anal. was used to monitor the concns. of glucose, lactate, ammonia, and asparagine in situ during bioreactor cultivation of CHO/SSF3 cells. Simple PLS calibration models were established using referenced in situ collected single-beam spectra of one immobilized culture. The models were applied to another immobilized culture and one suspension culture. In general, glucose predictions were unbiased for both culture types. Application of the lactate model resulted in a biased prediction during the first part of both cultures. Prediction results of the ammonia and asparagine models had both superior performance for the same type culture used in calibration. A neg. bias of approx. 1 mM was obsd. for all the predictions of ammonia in the suspension culture. [on SciFinder (R)]