The activity of Zn in low-melting {(1 - x(1) - x(2))Sn + x(1)Zn + x(2)In} alloys has been determined by the method of equilibrium saturation with metal vapour at T = 750 K. The total mote fraction of Zn and In was less than 0.25. As the method of equilibrium saturation is a comparative one, it is necessary to have an appropriate reference mixture. The {(1 - x)Sn - xZn} alloy was taken as the reference mixture. The interaction parameter epsilon(Zn)(In) was determined by a least-squares method. The experimental value of epsilon(Zn)(In) Zn was compared with the calculated value on the basis of a model of relative difference of ionic volumes. (C) 2003 Elsevier Science Ltd. All rights reserved.