Functional changes of the T-cell immune system in submandibularectomized (SMx) male mice of CBA/H strain were analyzed three or four weeks after treatment. Thymuses and spleens were weighed and morphologically examined by light microscopy. We tested proliferation rates of thymocytes and splenocytes (stimulated by Con A and PHA) and cytotoxic activity of T lymphocytes in SMx, CBA/H (H-2k) mice by means of the rejection test of allogeneic skin graft (Balb/c, H-2d) and a microcytoxicity to allo-antigens of EL-4 tumor cells (H-2b). Results showed a reduction of the weights of the thymus and spleen. However, there was increased functional capacity of the thymocytes--expressed as increased proliferation rates of the stimulated thymocytes, increased microcytotoxicity to allo-antigens of EL-4 tumor cells in vitro, and a reduction of the survival period of skin allografts in vivo. No morphological changes other than a reduction in both the cortex and medullar of the thymus were observed. The subpopulational changes within the T-cell system because of SMx indicate that the morphological atrophy could be just a consequence of SMx.