A modified version of the cantilever bending beam method is employed to subject a number of rigid and semi-rigid rod fibres to a gradient of axial compressive and tensile stresses. The molecular deformation of the filaments in tension and compression is monitored by scanning along the length of the filaments with a laser Raman microprobe. Strain hardening phenomena in tension and strain softening phenomena in compression are closely studied. Finally, a method for converting the Raman spectroscopic data into stress-strain curves in both tension and compression, is demonstrated.