The nature of the charge carriers in 'conducting' polymers is of considerable interest at present *RF 1,2*, largely on the basis of the technological potential of these materials for use as the semiconducting layer in field-effect transistors (FETs) and the emissive layer in light-emitting diodes  (LEDs). One of the main outstanding questions concerns the relative importance of intraversus inter-chain charge transfer in determining the overall rate of charge transport. Here we apply the pulse-radiolysis time-resolved microwave conductivity technique  to dilute solutions of a soluble dialkoxy derivative of the semiconducting polymer poly(phenylene vinylene), PPV, by which means we determine the one-dimensional intra-chain mobilities of electrons and holes on isolated polymer chains free from inter-chain interactions. The values so obtained-0.5 and 0.2 cm2 V sup -1 s sup -1 respectively-are considerably larger than the mobilities measured previously for bulk PPV-based materials [5-9]. This suggests that considerable improvement in the performance characteristics (in particular switching time and maximum current) of organic FET and LED devices should be possible if material purity and structural order can be better controlled.