11 patients with Hodgkin's disease in remission, including 7 patients with an initial stage III-IV, off treatment for at least 6 months, were tested for blood T lymphocyte functions. All were completely re-evaluated at the end of treatment to assess complete remission. The number of peripheral blood lymphocytes was below 1,200/cu mm 5/11 patients. Absolute numbers of E-rosette-forming T lymphocytes were decreased in 8 patients, whereas active rosettes were normal in 4/6. A slightly increased percentage of EAC rosettes, a marker for B lymphocytes, was found in only 2 patients. In vitro lymphocyte reactivity to a sub-optimal dose of PHA was studied in 9 patients. A statistically significant defect of lymphocyte transformation was observed in the patient group T lymphocytes. A membrane change is suggested rather than a true depletion. The persistance of such abnormalities long after treatment may raise the question of a complementary immunostimulating treatment in these patients.