The crystal structure of methyl β-xyloside has been worked out from X-ray diffraction data. The trial structure was obtained from a combination of vector syntheses and graphical methods. Refinement was carried out by Fourier syntheses, followed by least-squares and structure-factor calculations using 861 terms until R= 5·9%. The results confirm the configuration deduced by Haworth, with the pyranose ring in the strainless trans form. The mean bond lengths C–C 1·515 and C–O 1·417 Å with the angles all approximately tetrahdral. Molecules are linked in chains along the screw axis by hydrogen bonds.