The compaction of high-modulus melt-spun polyethylene fibres has been investigated for compaction temperatures above the optimum. After such treatment the specimens are liable to be non-uniform because of differential melting. Individual compacted fibres are observed to melt not only from the outside inwards, but also in certain internal regions, depending upon the availability of local free volume. The regions of different stability have been identified and inferences drawn concerning the structure of the initial fibres. It is suggested in particular that the longitudinal regions of deficit density (which exhibit cratering in transverse sections and melt before their surroundings) are a result of initial crystallization occurring within a rigid framework inside the fibre, possibly nucleated on a strained molecular network. The presence of banded recrystallization around residual fibres demonstrates that this phenomenon develops via interaction of neighbouring lamellae as they grow.