Vapour pressure and excess partial molar enthalpy were measured at 25 degreesC for solutions of methanol in H2O and artificial serum solutions. The mole fraction range studied was from 5 x 10(-4) to 5 x 10(-3). From the vapour pressure data, the partial pressures were determined by the Barker's and Boissonnas' methods. Various thermodynamic functions were then calculated from them. The curve-fitting (Barker's method) gave the osmotic coefficients very close to unity in all the cases, including serum solutions. The purely numerical method without resorting to any fitting function (Boissonnas' method), on the other hand, produced the osmotic coefficient significantly larger than unity in serum solutions studied. This is consistent with the findings by the earlier freezing point depression study on ethanol in human blood serum solutions. The partial molar enthalpy data indicated highly non-ideal behaviours also, particularly in serum solutions. The detailed mechanism causing non-ideality even at this dilute concentration range is yet to be elucidated. (C) 2003 Elsevier Science B.V. All rights reserved.