Isothermal vapor-liquid equilibrium relationships were determined at 950°C in a Colburn still for the ternary mixture water-n-propanol monoethanolamine and its three binary mixtures. The van Laar equation was found to describe the alcohol-water binary slightly better than the three-suffix Margules equation. The reverse was found to be true for the amine - water system. Because of a "concentration" effect, none of the equations employed in this investigation were very successful in predicting the amine-alcohol system. The Margules equation was found to have greater possibilities than either the van Lear or the symmetrical equations in predicting the ternary activity coefficients for this system. It was shown from this and a parallel investigation that an estimate of the accuracy of predicted ternary activity coefficients may be obtained from the correlation of the binary data.