In recent publications (D'Agostino et al., 2011; Moggridge, 2012a), we have proposed an equation to relate the mutual diffusion coefficient in a binary liquid mixture to the tracer diffusivities in the same mixture. The equation proved satisfactory for mixtures close to their consolute point as well as the general case of non-ideal mixtures; most of the available data relates to positive deviations from Raoult's law. In only one case, mixtures of acetone and chloroform, was the proposed equation not found to be consistent with the available experimental data. However, the tracer diffusivity data on which this assessment was based is old (1959 and 1967), of low accuracy and with few measurements to cover the range of compositions. For this reason we have re-measured the tracer diffusivities in acetone-chloroform mixtures at 25 degrees C with greater accuracy, by PFG-NMR, and used these measurements to re-examine the applicability of our equation to this system. We conclude that the proposed equation does in fact provide a good description of acetone-chloroform mixtures at 25 degrees C. This is of particular interest because acetone-chloroform shows a negative deviation from Raoult's law. The equation also gives a satisfactory fit for diethyl ether-chloroform and water-N-methylpyrrolidone (Moggridge, 2012a), both systems showing negative deviations from Raoult's law. (c) 2013 Elsevier Ltd. All rights reserved.