The aim of the present study was to evaluate the use of the radiopharmaceutical 123I-ioflupane in the diagnosis and differential diagnosis of Parkinsonism (P) and essential tremor (ET). Forty-three consecutive patients, aged 35-72 years, presenting symptoms and signs compatible with P, plus 11 normal volunteers, aged 40-60 years, were enrolled for the study. The radiopharmaceutical was injected iv in a dose of 185 MBq and tomographic acquisition in a single-headed Pegasys gamma-camera (ADAC, USA), 3-4 hours post injection was performed in order to evaluate the activity of the presynaptic nigro-striatal dopaminergic transporter. After reconstruction and reorientation, semiquantitative analysis was performed evaluating counts/pixel: a) in the striatum and its parts (caudate nucleus and putamen) of both hemispheres and b) in the visual cortex representing non specific binding. According to our results, all 21 individuals with ET were correctly evaluated with this method, whilst 21/22 patients were diagnosed as having P. No statistical difference concerning the binding of the radioligand to the striatum and its parts was found between normal volunteers and patients with ET. Based on the present results in 21 of our patients, the diagnosis and treatment procedure were changed, while in the remaining 22 patients diagnosis and treatment were confirmed. According to our data, as well as to the data from others, molecular imaging (SPET) with 123I-ioflupane can properly differentiate individuals with ET from those having P, in order to avoid an unnecessary use of drugs that may even cause side effects. All our patients were re-examined after eight months. At that time the above results and the treatment that was given to them meanwhile, were positively evaluated.