Disturbed motor control of the fingers, as revealed by the response to unexpected loading of an object held in a precision grip, or to finger perturbation during isometric holding, has been studied in patients with Huntington's disease (HD) and in normal subjects. In normal subjects unexpected loading elicited a reflex response (mean latency 73 ms) in the first dorsal interosseus muscle (FDI). This was accompanied by a clear increase in grip force, reaching a maximum at 200 ms, which stabilised block position. Index finger perturbation led to a long-latency reflex response in the FDI of all normal subjects. No such response was seen in the HD patients. The response to object loading, in contrast, was present, but significantly delayed (mean onset 95 ms; P = 0.0135). The response was qualitatively normal, with grip force reaching a maximum at 220-230 ms. It is suggested that the absence of the long-latency stretch reflex and the delay in the response to loading in HD patients may represent a reduction in somatosensory input to the cortex caused by disruption of basal ganglia structures.