Liquid–vapour composition curves have been determined for the systems aniline–monoethylaniline, monoethylaniline–diethylaniline, and aniline–diethylaniline. The experimental curve for aniline–monoethylaniline agrees quite well with the curve calculated using Raoult's law. However, the experimental curves for monoethylaniline–diethylaniline and aniline–diethylaniline show wide deviations from the calculated. From the shape of the experimental curves it appears that good separations of aniline, ethylaniline, and diethylaniline from one another may be effected by distillation with a reasonably good column. Improved separation could be obtained by distillation at reduced pressure.