Error-free pseudolinear transmission of 80 Gbit=s single-channel data over 840 km of standard fibre without optical regeneration, forwarderror correction or polarisation control is described. Gated autocorrelation and spectral measurements reveal that the performance is limited primarily by the optical signal-to-noise ratio, rather than dispersion or nonlinearity. Conclusions: We have demonstrated the successful transmission of 80 Gbit=s single-channel data over 840 km of conventional fibre without using any manual polarisation control or tracking in the transmitter or receiver. When the dispersion is fully compensated for, the performance is observed to be primarily limited by the attainable optical signal-to-noise ratio at the receiver.