Comparative investigation of immune status indices in patients with fever form of vernal encephalitis (group 1), with inapparent form with prolonged antigenemia (group III) and with short-term antigenemia (group II) was performed for the first time. Total 99 patients were under investigation. It was shown that in group I selective damage of immune system at T-level took place. In patients of group III immune system at all levels was less involved and humoral factor were changes. In patients in group II no significant change in immune system were registered. Activity of different immune correctors (thimalin, 4-iodoantipirine, leukinferon) was investigated in vitro. This preparations had stimulating effect in blood samples of patients with decreased immune status. In the patients with unchanged immune status no effect was demonstrated. The most prominent effect was revealed in the case of 4-iodoantipirine--interferon inducer.