To evaluate by MRI the area size and the degree of iron accumulation in basal ganglia nuclei that are implicated in the pathogenesis of Parkinson's disease (PD). 40 patients with idiopathic PD and 40 controls were examined on a 1. 5 Tesla MR imager, using a multiecho SE sequence 2000/20, 40, 60, 80, 100, 120, 140, 160 (TR/TE). The T2 relaxation time (T2) and the area of substantia nigra zona compacta (SNc), substantia nigra zona reticulata (SNr), putamen (Pu), globus pallidus external (GPe), globus pallidus internal (GPi), caudate nucleus (CN), locus coeruleus (LC) and subthalamic nucleus (STN) were assessed. The T2 of SNc (76. 8 +/- 6. 0) was lower and of Pu (79.5 +/- 6.0) and GPe (69.5 +/- 7.0) was higher in patients than in controls (78.6 +/- 3.8, 77.4 +/- 3.9 and 67.3 +/- 5.7, respectively), p < 0.05. The area of CN (125.9 +/- 20.2) and Pu (201.5 +/- 48.7) was higher in patients than in controls (110.7 +/- 21.5 and 180.1 +/- 41.1, respectively), p < 0.05. A more pronounced decrease in the T2 of SNc (73.6 +/- 8.9) was observed when the more affected side of patients was evaluated separately. In patients with disease duration > 5 years the T2 of STN (71.5 +/- 6.3) was lower and the area of Pu was higher (215.3 +/- 54.9) compared with those with disease duration < or = 5 years (75.8 +/- 10.9 and 190.9 +/- 41.0 respectively), p < 0.05. These findings suggest that dysfunction of the basal ganglia circuitry in PD may affect iron content not only in SNc but in STN, Pu and GPe as well. Compensatory sprouting of the remaining dopaminergic fibers could account for the increased area of the CN and Pu.