Raman spectroscopy has been used as a tool to monitor the microdeformation of a range of process-controlled fibres with different orientations. The mechanical properties of the fibres are shown to be related to the orientation parameter (< sin(2)theta >), and that by using the particular fibre spinning process (N-methylmorpholine N-oxide (NMMO)/cellulose), a plateau is reached, beyond which no improvements can be made. Clear shifts in the 1095 cm(-1) Raman band towards a lower wavenumber are observed upon the application of external tensile deformation, which are thought to relate to the molecular deformation of the cellulose chain. It is found that relationships are determinable between the rate of band shift with respect to strain of the 1095 cm(-1) Raman band and the orientation parameter. For the first time, a modified series model is related to the molecular deformation as revealed by Raman spectroscopy, and that the data for these fibres is consistent with a structure with a dominant amorphous fraction. Other high modulus cellulose fibres are shown to behave more like high performance polymer fibres such as poly(p-phenylene benzobisoxazole) (PBO) and poly(p-phenytene terephtalamide) (PPTA). The need, if high performance variants of these fibres are to be developed, to improve the microstructure of NMMO-cellulose fibres is discussed. (c) 2005 Elsevier Ltd. All rights reserved.