EPR studies at room and low temperatures of cooper(II) complexes of acetaldehyde thiosemicarbazone (AlTSC), pyruvic acid thiosemicarbazone (PTSC) and ribose bis-thiosemicarbazone (RibTSC) have been undertaken. Computer simulation of the EPR spectra has revealed differences in the magnetic parameters of the compound. Two species with different metal-ligand ratios were found to be present in PTSC. The higher degree of tetrahedral distortion displayed by the two mono-thiosemicarbazones with respect to RibTSC suggests that monothiosemicarbazone copper(II) complexes may be more effective superoxide dismutase-like mimics than bis-thiosemicarbazone complexes are.