Concanavalin A-induced lymphocyte capping was studied in 30 patients with Huntington's disease (HD) and 39 controls. A significant decrease in lymphocyte capping was seen in the 24 patients with HD less than 60 years of age compared to 25 age-matched controls (p less than 0.01); above age 60, differences between patients with HD and controls were not significant. These findings lend support to previous observations that generalized membrane abnormalities are present in patients with HD. Studies of HD lymphocyte capping may permit a detailed analysis of membrane function in cells that are readily obtained from living patients.