Analytical pyrolysis was used to determine blend levels in cotton/polyester yarns. Instead of trying to separate the compounds created by pyrolysis, gas chromatographic conditions were set to move the pyrolyzates quickly thorough the column. Measurement of the total area of the peaks was simple and reproducible. By pyrolyzing known specimens of pure and blended fibers, a calibration chart and regression curve were created that allowed unknown specimens to be pyrolyzed and their blend ratios to be calculated. The weights of the specimens tested and the areas of the resulting pyrograms were sufficient to give accurate and reproducible results in a short time.