The surface pressure-area (pi-A) isotherms of N-hexadecyl-8-hydroxy-2-quinolinecarboxamide (HHQ) monolayers at the air-water interface on subphases containing metal ions were investigated. The properties of the HHQ monolayer are dependent on the electronegativity, size, nuclear charge and the structure of the valence shell of the metal ion. At the air-water interface the amphiphilic HHQ with its complexing head group in contact with the aqueous phase can form metal complexes with many metal ions present in the aqueous phase. The formation of HHQ-metal complexes leads to changes in the area per HHQ molecule and the collapse pressure, as well as changes in the UV-visible absorption spectra of the monolayer assemblies.