The reliability of a method for the determination of missing group interaction parameters for the UNIFAC model(1) proposed by Gani et al.(2) was carefully examined. In this method, called CI-UNIFAC, the missing group interaction parameters are determined by means of connectivity indices. Such a method would be very desirable since it would save a lot of time and money spent for measuring VLE data to fill the gaps in the UNIFAC parameter matrix. Because of the great importance of distillation processes for the chemical industry, mainly the results for vapor-liquid equilibria (VLE) were investigated using the data stored in the Dortmund Data Bank and VLE data measured. There are examples it? which the method works quite well, but often the procedure leads to poor results. 0 2009 American Institute of Chemical Engineers AlChE. J. 55: 1614-1625, 2009