The peripheral blood lymphocytes of subjects of old age can be characterized as follows: deteriorated immunoglobulin synthesis under PWM stimulation, improved immunoglobulin synthesis under autoantigen (DNA) addition, increase in the anti-DNA auto-antibody synthesis, 4. higher sensitivity of the PHA-induced lymphocyte proliferation to prednisolone. The in-vitro methods have a model character for further investigations on the regulation of the immunological system and its possible therapeutical influencing.