Empirical models have long been available for estimating the Newtonian viscosity of single-phase silicate melts from composition in terms of oxide components [Bottinga and Weill, 1972; Shaw, 1972>. These models are used regularly to estimate or parametrize viscosity in field studies and fluid dynamical calculations of magmatic transport. However, few independent viscosity measurements on multi-component melts of natural composition have been made to test the accuracy of the empirical estimation models. A series of experimental measurements of viscosity has been performed on a dacitic melt, using the technique of concentric cylinder rheometry. In the ranges of temperature and shear rate examined (1000 to 1150 ¿C and 0.013 to 7.43 s-1, respectively), the melt viscosity is found to be independent of shear rate. When the viscomentric results from the present study and those on a rhyolitic composition [Hochella and Brown, 1984> are compared with the results from the empirical models, the model of Shaw [1972> is found to represent both sets of experimental data better than that of Bottinga and Weill [1972>. This is presumably due to differences in the ranges of temperature and composition represented in the data used to construct the respective models. ¿ American Geophysical Union 1993