Standard neurology texts list a reduced blink rate as one of the clinical features of Parkinson's disease. However, there are few clinical studies which have quantified this clinical sign. Here we present the results of a quantified study in a cohort of cases and controls using a standard protocol. Cases meeting standard criteria for a diagnosis of Parkinson's disease were studied together with age- and sex-matched controls. Baseline data included age, sex, duration of disease, Hoehn and Yahr stage, mini-mental state examination and treatment. Subjects were videoed undertaking three different tasks: being interviewed, watching a video, and reading from a book. Blink rates were calculated as a mean 'per minute' figure for each of the three tasks. A meta-analysis of previous studies of blink rate was undertaken. A total of 20 cases and 41 controls were studied. A decline in blink rate with increasing age was seen for cases but not controls. A significant reduction in blink rate was seen in cases when compared with controls for each of the test conditions. Blink rates were highest in subjects when being interviewed and were lowest whilst reading a passage in both cases and controls. No effect of disease duration, severity or treatment was observed. We have quantified the reduction in blink rate which has long been recognised as a feature of Parkinson's disease. We have identified factors which determine blink rate within individuals. We have also been able to define normal and abnormal levels for blink rate which may be of value clinically and for future research.