Flow calorimetric measurements of the excess molar enthalpy H-m(E) of {yN(2) + (1-y)C3H8}(g) at standard atmospheric pressure over the temperature range T = (241.2 to 393.4) K, and of {yN(2) + (1-y)C4H10}(g) made over the temperature range T = (283.4 to 393.5) K are reported. The measurements were analysed using the spherical core Kihara potential and values of the cross-term second virial coefficient B-12 were obtained. The accuracy of the H-m(E) measurements is +/-0.7 J . mol(-1), and the accuracy of the B-12 values is no worse than +/-8 cm(3) . mol(-1). The H-m(E) measurements on these mixtures are recommended as test systems for checking the performance of low-pressure gas mixing calorimeters. Empirical equations for H-m(E) (y=0.5) over a range of temperature are given.