beta-CIT was labeled with 131I by the peracetic acid method. Cat model of Parkinsonism was set up with MPTP. Each of normal and PD model cats was given an injection of 74 MBq/0.5 ml 131I-beta-CIT into the femur vein. Then the blood samples were obtained at 4 h and 20 h, the radioactivity was counted with calibrator. The biodistribution data of 131I-beta-CIT in cat body was calculated (ID%/g). The cats were subjected to imaging at 0.5 h, 1 h, 2 h, 4 h, 20 h after the administration of radiopharmaceutical. The radioactivity in striatum and cerebellum was measured and striatal specific binding ratios were calculated. The Results showed that the radio chemical purity of 131I-beta-CIT was 97.62% +/- 0.31%. The 131I-beta-CIT remained stable for at least 4 h after incubation with water and serum respectively. Following intravenous administration in cats, 131I-beta-CIT showed high accumulation in striatum. The study of imaging in cats showed that striatal specific uptake of 131I-beta-CIT at 20 h after injection was 4.83 +/- 0.82 in normal cats and 2.92 +/- 0.66 in PD cats. There was a significant reduction of striatal tracer uptake in PD cats, compared to the controls. The results of biodistribution study was in agreement with the results of imaging study. These results suggest that beta-CIT is an ideal agent for dopamine transporter imaging and can be used for the diagnosis of Parkinson's disease.