We have a continuing interest in the structural role of lone-pair cations in glasses. Thallium oxide behaves unusually in borate glasses, not only in terms of its own environment, but also in its effect on the boron network. It is the only glass modifier which produces a positive deviation from model N4 behaviour, all others being negative. We propose a combined neutron diffraction, x-ray diffraction 11B and 203/205Tl NMR study of the thallium borate xTl2O¿(1-x)B2O3 glass system in order to establish how the thallium environment can produce the observed changes in boron coordination. We propose to carry out high-resolution neutron total scattering experiments on a range of glass compositions from x = 0.05 to x = 0.45. The NMR data will provide some constraints on the fitting of the first B-O and Tl-O correlations and neutron/x-ray difference plots will help resolve the Tl correlations.