Complex studies were carried out on humoral and cell mediated immunity among persons over 60 years of age and persons aged 18-40. Humoral immune responses were not profoundly disturbed in the group of older persons. The level of isoagglutinins was lower in older subjects, but the level of immunoglobulins and antibodies to widespread bacterial and virus antigens (S. typhi O, Kunin's CA, parainfluenza types I, II and III) was the same in both groups. Cell mediated immunity was more greatly changed. Response to PPD in skin tests, lymphocyte stimulation tests, and the migration inhibition test was reduced in older subjects. Also, in this group, PHA in lymphocyte stimulation tests and the number of E-rosette forming cells was lower than among younger adults. However, responses to other antigens in skin tests, lymphocyte stimulation tests, migration inhibition tests (Candida albicans, SK-SD, Trichophyton) and responses to other stimulants of the lymphocyte stimulation tests (Con A,PWM) were well preserved in older subjects