AbstractE.s.r. spectra of spin‐labelled poly(vinyl acetate) plasticised to varying extents with dibutyl phthalate have been analysed to yield the temperature,T50G, at which the separation of the extrema is 50 G. As in the case of spin‐probed, plasticised poly(vinyl acetate), the reciprocal ofT50Gshows a linear dependence on the weight fraction of polymer. This observation supports the view that in the region ofT50Gthe label responds to the glass‐to‐rubber relaxation. At temperatures immediately belowT50Gthe low‐field peak in the spectrum is split, indicating that motion of the label occurs with a distribution of correlat