We applied quantitative methods to measure extrapyramidal signs in 50 Alzheimer's disease (AD) patients and 40 age-matched control subjects. We measured tremor using accelerometers, bradykinesia using computer-detected reaction times (RTs) and movement times (MTs), and rigidity using a strain gauge linked to a movable arm rest. We excluded subjects with a clinical diagnosis of Parkinson's disease and subjects who required antiparkinsonian, neuroleptic, or anxiolytic medications. Aside from rigidity in two patients, there were no extrapyramidal signs on clinical examination. Based on electrophysiologic measures, however, there was a significant increase in muscle tone (p < 0.001), RT (p < 0.01), and MT (p < 0.03) in AD patients as a group compared with control subjects. Within the AD group, muscle tone and MTs increased across clinical stages of dementia severity (p < 0.05). Tremor frequency and amplitude were normal in AD subjects. These data indicate that quantitative neurophysiologic measures are superior to conventional clinical examinations in detecting extrapyramidal signs in AD. The pathologic substrates of extrapyramidal signs in AD are uncertain but seem to be linked to the degenerative AD process.