Using a laser monitoring observation technique, solid-liquid equilibria in the systems benzoic acid + p-toluic acid + chloroform at 303.15 K, benzoic acid + p-toluic acid + acetic acid at 343.15 K, and terephthalic acid + isophthalic acid + N,N-dimethylformamide at 343.15 K have been investigated. The solid-liquid equilibrium phase diagrams for the three systems are plotted on the basis of the experimental data obtained.