Radiation therapy seems to induce depletion of lymphocytes, which are very important cells for immunity response. The lymphocyte phenotype was studied in 41 non-pretreated patients with normal immunological parameters who received postoperative radiation therapy for breast, mediastinal or pelvic cancer with at least 50 Gy/25 fractions. The functional immunological assessment was analyzed by Multiskin test (Merieux) too. The lymphocyte phenotype was determined on whole-blood lysate employing an Ortho double-fluorescence cytofluorimeter. All patients, after radiation treatment, exhibited decrement in absolute and percent lymphocyte subpopulations; the Multiskin test demonstrated simultaneous change in skin-test response. The results are highly significant (p 2-tailed area less than 0.0001) for absolute cells count and skin-delayed response test, but percent variations are not significant when verified by t-test.