The equilibrium pressure of mixtures of {xCH(3)F + (1-x)HCl} has been measured at temperatures of 159.01 K and 182.33 K by the static method. The measurements cover the entire composition range. The system is markedly non-ideal, exhibiting a minimum azeotrope near x = 0.55 at both temperatures. The excess molar Gibbs energy is an almost symmetrical function of composition giving G(m)(E) (x - 0.50,159.01 K) = -(924 24)J -mol-l and G(m)(E)(x = 0.50,182.33K) = -(846 +/- 15) J.mol(-1). The mean value of the excess molar enthalpy H-m(E) at the two temperatures, as assessed from the G(m)(E) values for the equimolar mixtures, is relatively large and negative: H-m(E) (x = 0.50) = -(1456 +/- 290) J.mol(-1). Amongst the binary mixtures of liquefied gases studied so far the high negative values of these excess functions are most unusual, suggesting that solvation between the molecules of the two components may take place in the liquid mixture. The results have been compared with estimates from the chemical theory of solutions.