The examination of 60 patients with vascular dystonia (VD) and immunological disorders shows that secondary immunodeficiency is not a stable condition. It is associated with seasons of the year and VD variants. Secondary immunodeficiency is more pronounced in winter. A correlation exists between mixed vegetative vascular dystonia and combined T-lymphocyte secondary immunodeficiency in winter. The findings may help in planning immunotherapy in "critical seasons" for patients with vegetative disorders.