A vibrating-wire viscometer and a single-sinker densimeter were simultaneously used to determine accurate eta rho pT data for normal butane. Seven isotherms were measured between (298.15 and 448.15) K up to maxima of 91 % of the saturated vapor pressure for the subcritical and of 30 MPa for the supercritical isotherms. The combined expanded uncertainty (k = 2) in density is 0.2 %, except for the low-density region. The data agree within +/- 0.4 % with densities for the equation of state by Bucker and Wagner, excluding the near-critical region due to the strong influence of allocation errors for temperature and pressure. The deviations for the near-critical isotherm 428.15 K amount to +8.5 %, distinctly higher than the total expanded uncertainty of the density data (2.4 %). The viscosity measurement is less influenced in the near-critical region by allocation errors for temperature and density so that the total expanded uncertainty is 0.6 %. The new data were compared with viscosity correlations of Younglove and Ely, Vogel et al., and Quinones-Cisneros and Deiters. Maximum deviations between +16 % and 7 % at 428.15 K and densities 150 < rho/kg.m(-3) < 300 exceed seriously the expanded uncertainties of 6.0 % for the three correlations. The effect of about +1 % for the critical enhancement is obvious for 428.15 K. The present data should be used to generate a new viscosity correlation.