A new approach for the indirect detn. of cell concn. in the case of nonconstant metabolic rates has been developed. The specific glucose-uptake rate was shown to be nonconstant in batch cultures of free suspended and immobilized CHO SSF3 cells. Time-independent models correlating the specific rate to the limiting substrate concn. were established, thus providing a continuous detn. of the specific rate through online measurement of the limiting substrate. The method could be applied to det. online cell concn. in both free suspended and immobilized cell cultures. Results were verified off-line by crystal violet nuclei counting. The predicted cell concn. was in very good agreement with the off-line ref. during the whole exponential-growth phase, until the specific glucose-uptake rate tended to zero. [on SciFinder (R)]