Mass-analysed threshold ionisation (MATI) spectra of the Ar NO complex have been obtained for the first time. These spectra have been used to determine unambiguously the nature of three bands detected by resonance-enhanced multiphoton ionisation (REMPI) spectroscopy via the A state of Ar NO. The features are should to originate from vibrationally excited states of Ar . TO in its electronic ground state. The assignment is in agreement with recent theoretical calculations.