The systems triethylamine–methylethylketone–dimethylsulfoxide and triethylamine–methylethylketone–formamide have been studied by the methods of isothermal equilibrium and thermal analysis. At least in the case of the system triethylamine–methylethylketone–dimethylsulfoxide, the equilibrium conditions have been completely established with respect to concentration and temperature. From these data a solid model can be constructed, as was previously done for the system nicotine–water–methylethylketone. It appears that the miscibility is greater in the system involving dimethylsulfoxide than in the system involving formamide.