This article presents a study of the behaviour in solution of 1-butyl-4-methylpyridinium tetrafluoroborate [b4mpy][BF4] in water and in the first five alkanols of the series methanol to pentan-1-ol. The excess enthalpies, H-m(E) and volumes, V-m(E) were determined at the temperatures (298.15 and 318.15) K. At these temperatures, the [b4mpy][BF4] was completely miscible in water, methanol, and ethanol, but only partially miscible in the other alkanols. A solubility study was carried out and the (liquid + liquid) equilibria of the ([b4mpy][BF4] + alkanol) systems were experimentally determined, evaluating zones of complete miscibility and determining the UCST in each case. The mixtures with water gave positive values of H-m(E). The and V-m(E), being also positive the changes of these quantities with temperature. The mixtures with alkanols gave values of H-m(E) > 0 and V-m(E) < 0, and for these binary mixtures (dH(m)(E)/dT)(p) > 0 and (dV(m)(E)/dT)(p) < 0. For all cases, results were interpreted and compared with data obtained in mixtures with another isomer [b3mpy][BF4]. Excess properties were correlated with a suitable equation and the area and volume parameters were calculated for [b4mpy][BF4]. (C) 200E Elsevier Ltd. All rights reserved.