The width of substantia nigra (SN) in 59 cases with idiopathic Parkinson's disease as well as 21 normal controls was analyzed by T2 weighted image (T2WI) of 1.5 Tesla high-field magnetic resonance image (MRI). All patients and controls underwent MRI with the spin-echo sequences used TR/TE: 3000/30 (short TE), and TR/TE:3000/80 (long TE), in 5-mm-thick volumes. The width between the red nucleus and the cerebral peduncle showing low signal intensity areas was measured as that of SN and its ratio to the distance from the aqueduct to the midline of the cerebral peduncle was also measured. The calculated values of the width of SN and its ratio were analyzed by Mann-Whitney test. The significant reduction in the width of SN and its ratio in Parkinson's disease were disclosed as below; the mean calculated values of the width of SN were 2.95 +/- 0.51 mm in controls, 2.68 +/- 0.99 mm in Parkinson's diseases on long TE images (P less than 0.01), and the mean ratio of the width of SN were 13.58 +/- 4.21% in controls, 10.52 +/- 3.07% in Parkinson's diseases on long TE images (P = 0.0002). The narrowing of SN in Parkinson's disease was more prominent in men, and advanced cases with Yahr stage III and IV. Considering that the pars reticulata, which is normally containing iron, shows low signal intensity on long TE images, the width of pars compacta could be measured more precisely on this sequences. The evaluation of the ratio of SN in midbrain on long TE images seemed to be more sensitive than the calculated values in detecting the narrowing of SN and pars compacta in Parkinson's disease.