The basic ideas of a novel way to simulate electron paramagnetic resonance (e.p.r.) spectra of spin-labelled polymers are described. The simulation method has been applied in the analysis of the e.p.r. spectra of dry spin-labelled poly(octyl isocyanate) (POIC). POIC is a semiflexible, helical polymer capable of forming a thermotropic Liquid crystalline phase. The spectra of a fractionated POIC sample have been analysed in order to find out how the mobility and flexibility of the chain change with increasing temperature, when the polymer turns from the semicrystalline into the liquid crystalline state. The results imply that the sample contains both helical and random chain sequences through the whole temperature range studied. However, the proportion of the helical sequences is dependent on temperature.