A series of studies demonstrated a possible relationship between eye-blink rate and central dopamine activity. First, apomorphine and other dopamine agonists acutely increased blink rate in monkeys, an effect blocked by sulpiride. Secondly, parkinsonian patients with levodopa-induced dyskinesia exhibited twice the mean blink rate (21 blinks/min) of other parkinsonians (11 blinks/min, P less than 0.002) whereas the more symptomatic of the nondyskinetic patients had a very slow rate (3 blinks/min, P less than 0.01). Thirdly, schizophrenic patients had an elevated mean blink (31 vs 23 blinks/min for normals, P less than 0.05) which was normalized by neuroleptic treatment. Thus, the correlation with central dopamine activity may also prove clinically useful in selected neuropsychiatric disorders.