The electronic properties of the Ti_1-xSc_xNiSn and Zr_1-xSc_xNiSn solid solutions were investigated using the Korringa-Kohn-Rostoker Green's function method within the coherent potential approximation. The calculations confirm the metallic type conductivity of the Sc content compounds as evidenced from electrical resistivity measurements and show that the main source of the electron conductivity originates from the d-electrons of Ti(Zr) and Sc.