A technique has been developed which allows the determination of a two-photon absorption cross-section to be made relative to the Raman scattering cross-section in nitrogen. Spatial and temporal effects associated with the lasers are ratioed out to give a result in-dependent of laser parameters. The necessary theory to extract a cross-section from the measured ratio of a Coherent Anti-Stokes Raman Scattering (CARS) signal in N2 to a four-wave mixing signal in NO has been developed. The technique has been demonstrated on the R22 S12(J" = 9 1/2) line in NO and a cross-section of (2.9 + 1.8) x 10-49 cm4-s was determined. This technique appears to be applicable to a number of other diatomic molecules.