Abstract Objective Direct measurement of chemical constituents in complex biologic matrices without the use of analyte specific reagents could be a step forward toward the simplification of clinical biochemistry. Problems related to reagents such as production errors, improper handling, and lot-to-lot variations would be eliminated as well as errors occurring during assay execution. We describe and validate a reagent free method for direct measurement of six analytes in human plasma based on Fourier-transform infrared spectroscopy (FTIR). Design and methods Blood plasma is analyzed without any sample preparation. FTIR spectrum of the raw plasma is recorded in a sampling cuvette specially designed for measurement of aqueous solutions. For each analyte, a mathematical calibration process is performed by a stepwise selection of wavelengths giving the optimal least-squares correlation between the measured FTIR signal and the analyte concentration measured by conventional clinical reference methods. The developed calibration algorithms are subsequently evaluated for their capability to predict the concentration of the six analytes in blinded patient samples. Results The correlation between the six FTIR methods and corresponding reference methods were 0.87<R2<1.00. The interassay imprecision meets international quality criteria for all the six analytes. The linearity of the FTIR methods extends over the clinically significant concentration ranges. Visible hemolysis and icterus have some influence on the measurements. Plasma samples can be stored at 2–8°C for at least 8days before the analysis. Conclusions The developed FTIR methods use a simple and robust technology to achieve stable and accurate results that meet international quality criteria for the measurement of glucose, triglycerides, urea, cholesterol, albumin and total protein in human plasma.