DOPA-melanin and its complexes with netilmicin and metal ions (Zn2+,Cu2+) were examined by EPR spectroscopy. Broad EPR lines of o-semiquinone free radicals and paramagnetic Cu2+ were measured. Netilmicin slightly increased free radicals concentration in DOPA-melanin. Diamagnetic Zn2+ and paramagnetic Cu2+ ions increased and decreased, respectively, free radical concentrations in melanin-netilmicin complexes. Higher free radical concentrations were determined for (melanin-Zn2+)-netilmicin complexes than for (melanin-netilmicin)-Zn2+. Free radical concentrations were lower in (melanin-Cu2+)-netilmicin complexes than in (melanin-netilmicin)-Cu2+. Slow and fast spin-lattice relaxation processes were found for free radicals and Cu2+ systems in the samples. Netilmicin and Cu2+ increased spin-lattice relaxation time in melanin. (C) 2004 Elsevier B.V. All rights reserved.