The paper explores the measurement, using X-rays, of the micro-fibril angle of the cellulose fibres in the S2 layers of the cell walls of soft-wood, particularly pinus radiata. It is demonstrated that unambiguous values of the micro-fibril angle can be obtained from small angle X-ray scattering patterns if the X-ray beam is directed at 45 degrees to both sets of cell walls, with the cell axes vertical. The theory of the method is presented and justified. Examples of the measurement of the micro-fibril angle in pinus radiata specimens are given. It is demonstrated that the scattering patterns obtained with the X-ray beam directed normal to one set of cell walls are not capable of yielding micro-fibril angle values. The wide-angle diffraction pattern from the (002) planes with the X-ray beam equally inclined to both sets of cell walls has been analysed. The analysis has been justified experimentally and it is shown that the S2 fibres give rise to eight intensity maxima round the (002) circle and that the azimuthal angles can be related to the micro-fibril angle. It has not been possible to resolve the eight peaks. Wide-angle diffraction patterns revealed four peaks, each comprising two merged adjacent peaks. The azimuth angle at the centre of each of the four peaks is the average of those for the two constituent peaks. It is demonstrated that values of the micro-fibril angle can be obtained from this average azimuth angle.