We propose a new method to search for axion-like particles ( ALPs ) based on the gamma-rays produced concomitant with high-energy astrophysical neutrinos . The existence of high-energy neutrinos implies production of gamma-rays in the same sources . Photons can convert into ALPs in the sources ’ magnetic fields , and will travel as ALPs through extragalactic space . Back-conversion in the Milky Way ’ s magnetic field leads to a diffuse anisotropic high-energy photon flux that existing and upcoming gamma-ray detectors , like HAWC , CTA , and LHAASO can detect . This method probes unexplored ALP parameter space , with LHAASO being realistically sensitive to couplings above 10 ^ { -11 } { GeV ^ { -1 } } and masses up to 3 \times 10 ^ { -6 } eV in ten years . Our technique also explores viable ALP dark matter parameter space .