The space charge distribution, an important electrical property, has been studied by means of the thermal step (TS) method for some poly(vinyl chloride) (PVC) samples containing polyethylene (PE) sequences, as the result of hydrogenation reaction of PVC with H4LiAl to conversions ranging from 1 to 12%. Both the preparation and the characterization of the samples by C-13 n.m.r. are to be published elsewhere. The aim of the present work is to investigate the effect of the changes in molecular microstructure, whether relevant to the tacticity of PVC or to that occurring when CH2 groups are substituted for CHCl groups, on the nature and distribution of space charges which are formed upon applying an electrical field. The contribution of the PE structure to the overall space charge distribution could be evidenced by comparing the results obtained to those extensively published on tacticity microstructure/space charge relationships for PVC. Since hydrogenated PVC may be considered as a precursor of PE, the results provide novel information about the space charge behaviour of the latter polymer.