This study is the first to assess the analytic potential of Fourier-transform infrared (FT-IR) spectroscopy in determining exercise-induced metabolic changes, such as glucose and lactate serum concentrations, with single 50 microL blood microsamples. One-hundred ninety-eight capillary blood samples were taken at rest (rest serum) and after rowing exercises at different intensities (exercise serum) to obtain a wide range of lactate concentrations. A quantitative method is described with FT-IR spectroscopy involving only dilution and dessiccation of serum samples. Within serum spectra, an absorption band was strongly specific of glucose (1033 cm(-1)) that allowed the determination of its concentration (r = 0.97; P < .001 with reference values). Once we had substrated measured glucose absorption in serum spectra, one other absorption band seemed to be specific for lactate (1127 cm(-1)), which allowed the determination of the concentration of this metabolite (r = 0.96; P < .001 with reference values). The convenience of a capillary blood sampling with the strong accuracy of FT-IR measurements is of particular interest for medicinal and biologic concerns.