The excess molar enthalpies of (acetonitrile + butan-2-one) and (methanol + acetonitrile + butan-2-one) were measured at T = 298.15 K and atmospheric pressure using a flow microcalorimeter. The experimental results are correlated with polynomial equations and compared with those calculated from associated solution models taking account into self-association of methanol and acetonitrile as well as solvation between unlike molecules and a non-polar interaction term. (C) 2001 Academic Press.