The deposition of a fourfold positively charged tetrakis(4-methyl pyridinium) porphyrin (H(2)TMPyP) and its metal derivatives on glass surfaces from basic aqueous solutions has been studied by optical and ion beam techniques. Upon exposure to a buffered porphyrin solution, the glass surface is initially almost completely coated with a monomolecular porphyrin layer (5 X 10(13) molecules cm(-2)). Subsequently the area of the glass surface available for deposition of porphyrins increases due to leaching by the buffer solution, resulting in an almost linear increase of the amount of adsorbed organic material. Adsorption is limited to a monolayer in the presence of trace amounts of zinc ions.