A thermodynamic method is presented which makes possible the correct derivation of solidus and liquidus curves from a set of experimental liquidus points. In an iterative procedure, which is based on the equal-G curve and which uses intermediate phase diagram calculations, the liquidus of the calculated phase diagram is made to run through the experimental liquidus points. In addition, information about the thermodynamic mixing properties of the system is obtained_ Results are given for the systems p-dichlorobenzene + p-dibromobenzene, KzCOs + KzS04, KCI + NaCI.