Advances in middle infrared technology are leading researchers beyond the Fourier transform infrared spectrometer and to the quantum cascade laser. While most research focuses on gas-phase detection, recent research explores its use for condensed-phase matter studies. This work investigates its use for monitoring biologically relevant samples of glucose in serum. Samples with physiological glucose concentrations were monitored with a laser at 1036 cm -1. A 0.992 R 2 linearity value was observed. In addition, using another laser at 1194 cm -1 as a measure of the background spectroscopic characteristics, a linearity of 0.998 R 2 was observed. The average predictive standard errors of the mean (SEM) were 32.5 and 24.7 mg/dL, respectively, for each method. Quantum cascade lasers could be used to develop middle infrared devices for uses beyond the confines of the laboratory. © 2005 Society for Applied Spectroscopy.