The enthalpies of mixing of liquid (Co + Cu + Zr) alloys have been determined using the high-temperature isoperibolic calorimeter. The measurements have been performed along three sections (x(Co)/x(Cu) = 3/1, 1/1, 1/3) with x(Zr) = 0 to 0.55 at T = 1873 K. Over the investigated composition range, the partial mixing enthalpies of zirconium are negative. The limiting partial enthalpies of mixing of undercooled liquid zirconium in liquid (Co + Cu) alloys are (-138 +/- 18) kJ . mol (1) (the section x(Co)/x(Cu) = 3/1), (-155 +/- 10) kJ . mol (1) (the section x(Co)/x(Cu) = 1/1), and (-130 +/- 22) kJ . mol (1) (the section x(Co)/x(Cu) = 1/3). The integral mixing enthalpies are sign-changing. The isenthalpic curves have been plotted on the Gibbs triangle. The main features of the composition dependence of the integral mixing enthalpy of liquid ternary alloys are defined by the pair (Co + Zr) and (Cu + Zr) interactions. (C) 2015 Elsevier Ltd. All rights reserved.