The excess molar enthalpies h(m)(E) of the ethanol-propanal system have been measured at 298.15 and 318.15 K by means of an isothermal flow calorimeter. The pressure-effect on the h(m)(E) values has been investigated in order to compare these data with low-pressure vapor-liquid equilibrium data previously reported for the ethanol-propanal system. Values for h(m)(E) are very exothermic. Mixtures at 298.15 K exhibit a minimum of approximately - 7300 J mol(-1) at a mole fraction close to 0.5. Mixtures at 318.15 K exhibit a minimum of approximately -5000 J mol(-1) at a mole fraction close to 0.6. These values for h(m)(E) are similar to those previously found for the methanol-propanal mixtures.