The efficiency of SABRE strongly depends on the external magnetic field. Here we explore SABRE at ultra-low magnetic fields, which corresponds to the strong coupling regime (i.e., the difference of the Larmor frequencies of the nuclei is much smaller than their spin-spin coupling) of the protons originated from pH2 and magnetic heteronuclei, such as 13 C or N, in the Ir-complex. However, coherent polarization transfer occurs only in the vicinity of the avoided crossings of the spin energy levels; therefore, it requires the fine tune of the ULF strength depending on the spin-spin coupling topology of the considered SABRE complex. To determine the optimal ultra-low field, we measured the magnetic field dependences of photo-SABRE derived polarization levels for 1 H, C and 15 N in cis-and trans-ABZ (Fig. ). In fact, as trans-ABZ possesses polarization only through cis-ABZ these two forms yield the field dependences of the same shape, but with different amplitudes. Further, we present spectra and signal enhancement levels obtained with optimal values of the ULF for the corresponding nuclei. Although we initially aimed to hyperpolarize N nuclei of the substrate (a common case in SABRE studies), we also found substantial polarization of C nuclei (with the natural isotopic abundance) and relatively small polarization of 1 H nuclei in the very narrow range of fields below 300 nT. We attribute the latter to the extremely weak spin-spin interaction between the hydride protons and ABZ protons in the SABRE complex.