An adaptive calibration procedure is used to build selective multivariate calibration models for the measurement of glucose, lactate, glutamine, and ammonia in undiluted serum‐based cell culture media. This adaptive procedure removes metabolism‐induced covariance between these analytes in a series of calibration samples collected during the cultivation of PC‐3 human prostate cancer cells. Partial least‐squares calibration models are generated from single‐beam near‐infrared (NIR) spectra collected over the 4800‐ to 4200‐cm⁻¹ combination spectral range. Calibration models were generated with both the full spectral range and optimized spectral ranges. In both cases, the number of model factors was optimized and model validity was determined by comparing analyte concentrations predicted from a series of independent and unaltered samples that were obtained during a subsequent cultivation of the PC‐3 cells. Similar analytical performance was achieved with fewer model factors when the optimized spectral range was used. The lowest standard errors of prediction were 0.82, 0.94, 0.55, and 0.76 mM for glucose, lactate, glutamine, and ammonia, respectively. Different spectral ranges were optimal for each analyte and the optimized spectral range coincided with the distinguishing spectral features of the analyte. The results of this study demonstrate that NIR spectroscopy can be used effectively in the off‐line measurement of important nutrients (glucose and glutamine) and byproducts (lactate and ammonia) in a serum‐based animal cell culture medium. © 2002 John Wiley & Sons, Inc. Biotechnol Bioeng 77: 73–82, 2002.