Positron emission tomography and single photon emission computed tomography both now provide an objective means of quantitating loss of striatal dopaminergic terminal function in Parkinson's disease and of following disease progression. 18F-dopa positron emission tomography can also detect frontal changes in Parkinson's disease and preclinical disease in 30% of asymptomatic adult relatives of familial cases. Positron emission tomography, single photon emission computed tomography and proton magnetic resonance spectroscopy are all useful for distinguishing Parkinson's disease from atypical syndromes where diagnostic doubt exists.