Abstract The EPR spectra of single crystals of the tetrahedrally distorted tetradentate Schiff base complex, N, N'-bis(2-hydroxyacetophenone)-1,3-propanediimine Cu(II) and of its 63Cu(II) doped Ni(II) analogue were studied in an attempt to determine the effects of the tetrahedral distortion on the spin-Hamiltonian parameters and molecular orbital coefficients of the complex. The parameters in the usual doublet spin-Hamiltonian were found to be: Cu(II) complex; gx = 2.052 · 0.004, gy = 2.048 · 0.004, gz = 2.225 · 0.002; 63Cu(II) doped Ni(II) complex; gx = 2.045 · 0.004, gy = 2.043 · 0.004, gz = 2.216 · 0.002, Ax = 35.0 × 10−4 cm−1, Ay = 30.2 × 10−4 cm−1, Az = 190.4 × 10−4 cm−1. It was found that although gz seems to be unusually high, and Az unusually low, the values of the molecular orbital parameters and of the isotropic contact term fall within the range found for similar compounds which are not tetrahedrally distorted.