Excess molar enthalpies, H-E, for the binary systems of benzene or cyclohexane with 1,1-diethoxyethane at 323.15 K and with 2,2-dimethoxybutane at 303.15 K are presented. Additionally, infinite dilution activity coefficients for benzene and cyclohexane in 1,1-diethoxyethane have been measured between 293.08 K and 323.15 K. The heat of mixing measurements have been carried out by means of a commercially available Hart Scientific (model 7501) flow calorimeter with an estimated accuracy of better than +/-1% over the whole composition range. For the description of the experimental data a Redlich-Kister polynomial was used. The infinite dilution activity coefficients have been measured using the dilutor technique. The experimental results were compared with those predicted by the modified UNIFAC (Dortmund) model using the available interaction parameters for the "ether" group. The aim of this work is to supplement the available database for acetal systems required for the introduction the new "acetal" group in the modified UNIFAC (Dortmund) model.