The application of factor anal. in energy-dispersive x-ray fluorescence anal. (EDXRF) as a method for evaluation of elemental concns. and calcn. of net peak areas is demonstrated in 2 examples. A quant. principal component regression (PCR) anal. of S interfered with by Mo was performed by the XRF-spectra as input with a std. error of anal. (SEA) <0.2 mg/g for aq. and 3.6 mg/g for solid samples. By using PCR-predicted net peak areas as input for the empirical evaluation method developed by Lucas-Tooth and Price, the SEA for solid samples could be decreased to 2.3 mg/g. The comparison of PCR to partial least squares showed no significant difference.