The synchrotron-XRF microprobe set-up at HASYLAB, DESY (Deutsches Elektronen-Synchrotron, Hamburg, Germany) has been evaluated in terms of accuracy and precision of trace-element analysis using a standard-free fundamental-parameter approach to quantification. Six geological standard reference materials, including BHVO-1 and SY-3 glasses, were repeatedly analyzed over a period of one to three years. The precision of five replicate measurements at single locations in any sample, expressed as relative percent (standard deviation/mean × 100), is better than 1 % for the elements Cu, Zn, Ga, Rb, Sr, Y, Zr, Nb, Ba, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Hf, Ta, Th, and U, at concentration levels of several ppm. For SY-3 and BHVO-1 glasses, an accuracy between 0.25 and 14.0 % was obtained for elements from Cu (Z = 29) to U (Z = 92), except for Ho and Rb, where accuracies are 19 to 33 %. Detection limits are in the order of 1 to 10 ppm for the above elements. This makes the SYXRF microprobe well suited for studies of trace-element zoning and diffusion.