We succeeded in the culture of the thymic epithelium which obtained from the patients with various autoimmune diseases aged from 20 to 65 years whose thymuses should have already been involuted with decreased thymic function. The mean percentage of active rosette-forming cells significantly increased after the incubation with thymic monolayer culture medium. These observations suggest that thymic epithelia in autoimmune diseases produce thymosin-like factor(s) in culture medium.