Iron released from ferritin may trigger oxidative stress leading to progressive neurodegeneration of substantia nigra resulting in Parkinson's disease (PD). Change in the structure of ferritin may allow an easier efflux of iron. We compared with the use of ELISA the structure of ferritin (concentrations of H and L ferritins) in substantia nigra (SN) in ten cases of PD, six of incidental Lewy body (ILB) cases and 20 controls. SN concentration of L ferritin in ILB (50.6+/-11.5 ng/mg) and in PD (52.5+/-26.0) was lower than in control (97.9+/-54.9). H ferritin in PD (534.2+/-223.1) was higher than in ILB (336.9+/-87.7) and control (374.8+/-169.3). The decrease of L ferritin in SN in PD and ILB may suggest that the whole process of neurodegeneration starts with a higher availability of free iron, which is released from the ferritin shell.