The pulsed electron paramagnetic resonance (EPR) technique of V-51 electron spin echo-electron nuclear double resonance (ESE-ENDOR) has been used to measure the nuclear quadrupole coupling constants of a series of five-coordinate vanadyl complexes containing Schiff base ligands with geometries ranging from distorted square pyramidal to distorted trigonal bipyramidal. Vanadium nuclear quadrupole coupling constants are sensitive to the coordination geometry of the vanadyl ion, and thus sensitive to the structural distortions within this series of complexes. V-51 ESE-ENDOR has been shown to be a probe of the coordination geometry of vanadyl complexes. Such a spectroscopic probe should prove useful in the investigation of vanadyl of unknown coordination geometry, such as may be found in the interaction of the vanadyl ion with biomolecules.