A detailed experimental study of the pressure and density of He - N-2 mixtures at 0 degrees C, 25.0 degrees C and 50.0 degrees C is reported. The pressures are measured with a dead-weight tester. The densities are determined from knowledge of the precise volume and weight measurement of the mixtures. Statistical analysis of the experimental data yielded very precise values for the second and third density virial coefficients. Experimentally determined virial coefficients are compared with those of the literature. Unlike interaction second virial coefficients, B-12, are determined from the mixture virial coefficients by using the like interaction virial coefficients, B-11 and B-22, of the pure components. The deduced B-12 values agree very well with those computed from potential functions with quantum corrections.