The method described utilises the effect that in many commercially available laser diffractometers a laminary flow of the suspension medium in the measurement cell exists. However, data analysis carried out using commercially available laser di diffractometers is normally based upon the assumption that there is a statistical orientation of the particles in the measurement volume. The resulting diffraction patterns are, therefore, assumed to be centrosymmetric and ring-shaped. As a consequence, the detectors commonly used only record parts of the diffraction patterns. Based upon these assumptions, it is accepted that grain size analysis of fibrous particles gives an equivalent diameter between length and diameter. First experiments carried out using a Malvern Mastersizer X showed that fibres align in the flow direction. Analysis of the entire diffraction pattern should, therefore, provide information about the length and diameter of the fibres.