Previous studies from this lab have demonstrated the presence of a novel absorption in infrared spectra of synovial fluid films (2337-2343 cm(-1)) which was suggested to arise from CO2 trapped within the organic matrix left after drying. In the present paper, we establish the presence of this absorption in a wide range of biological fluids, tissues, and cell suspensions, Results of studies with a range of common biological materials suggest that the CO2 interacts nonspecifically with the protein components of cells and fluids. Experiments with C-13-labeled glucose clearly demonstrate that this ubiquitous absorption is attributable to CO2 produced by glucose breakdown within cells, presenting the interesting possibility of monitoring cellular metabolism by infrared spectroscopy.