In numerous cases the technique of Fiberoptic Evanescent Wave Spectroscopy (FEWS) offers great advantages over regular IR spectroscopic methods. It provides an easy way for measuring the absorption spectra of highly absorbing or highly scattering samples. With FEWS one can perform measurements in situ and in real time and this is potentially useful for measurements on biological samples or for the monitoring of chemical reactions. In the present work, the FEWS technique was used to analyze human blood serum using a Fourier Transform Infrared Spectrometer. A special cell based on IR transmitting non-toxic silver halide fibers was designed. Further improvements in the analysis were obtained by adopting some multivariate calibration techniques that have already been used in clinical chemistry. The blood constituents analyzed were: urea, total protein, cholesterol, uric acid and calcium. Good agreement between our results and the ordinary chemical and enzymatic methods was obtained.