This paper highlights the importance of both surface and internal ( bulk) structure of polypropylene (PP) melt extruded monofilament fibres and the dependence of structure on processing conditions. Gravity spun and as-spun fibres showed similar spherulitic surface structure but Wide Angle X-ray Scattering (WAXS) results indicated that the overall fibre crystallinity was contrasting for the two fibre types. From analysis of longitudinal and transverse fibre cross sections using Scanning Probe Microscopy (SPM) and Environmental Scanning Electron Microscopy (ESEM) it was found that gravity spun fibres showed a shish-kebab type structure in contrast to the macrofibrillar internal structure of the as-spun variant. In situ tensile testing gave powerful evidence to suggest that deformation in the necking region for the gravity spun fibres was due to the composite behaviour of the spherulitic surface and the internal shish-kebab structure. (C) 2003 Kluwer Academic Publishers.