Patients with Darier's disease have frequently been observed to develop severe bacterial and viral infections. Previous studies have indicated some derangement in the immune system, even though no consistent or specific abnormality has yet been demonstrated. We performed the results of immunologic studies in 10 patients with Darier's disease. In each patient humoral immunity and cell-mediated immunity (in vivo and in vitro) were evaluated and leukocyte chemotactic function was assayed. Humoral immunity was normal; as regards clusters of differentiation (CD), a slight increase in CD4 lymphocyte subpopulations was observed in 7 patients and of CD4/CD8 ratio in 1 case. The lymphocyte responses to phytohemagglutinin and concanavalin A were normal, whereas the response to pokeweed mitogen was decreased slightly, but not significantly. Normal random and chemotactic mobility was found in all the patients except one. The data obtained do not show important immunological alterations. Our patients did not have a high propensity to develop severe infections and this may explain the absence of significant immunological derangement. Our data confirm that no immunological derangement is associated with Darier's disease.