The inhibition of protein-tyrosine phosphatase 1B (PTP1B) is a potential target for treatment of type 2 diabetes. Vanadium and zinc metal coordinated complexes have insulin-enhancing activities, and while vanadium compounds inhibit PTP1B, little is known on the mode of action of zinc compounds. In this study we developed an automated PTP1B inhibition assay that allows for a rapid assessment of the PTP1B inhibition strength of candidate compounds. Synthetic vanadium(IV) and zinc(II) complexes were evaluated: IC₅₀ values for vanadium complexes ranged from 0.06 to 0.8m whereas for zinc compounds, values were above 10 m. Vanadium sulfate, a non-conjugated inorganic salt, had stronger inhibition activity than any of the conjugated metal complexes.