57Fe Mössbauer spectroscopy at different temperatures has been used to characterize the nature of purified human neuromelanin isolated from the substantia nigra. The quantitative determination of iron(III) by estimation of the overall area of the Mössbauer spectrum at room temperature reveals an iron content of 2.8 +/- 1.4%. No subspectra corresponding to divalent iron could be observed in these spectra. The derived Mössbauer parameters lead to the conclusion that the iron sites in the human neuromelanin are similar to those of human hemosiderin (or ferritin). However, owing to the water insolubility of the purified neuromelanin, it must be concluded that the neuromelanin hemosiderin (or ferritin) is bound in a protein matrix that makes it insoluble and difficult to stain histochemically. This protein attachment to neuromelanin is important in that it is what makes it different from synthetic dopamine melanin.