Recent demonstrations that naive T cells proliferate after transfer to lymphopenic hosts have led to the theory that active homeostatic mechanisms fill the peripheral pool of naive T cells. To extend these data, we injected naive CD4(+) T cells from AND TCR transgenic mice (H-2(b/b) or H-2(k/k)) into CD3 epsilon-deficient mice, and studied the absolute number, phenotype and functional capacities of the transferred lymphocytes, from the first days to a few months after transfer. Proliferation of naive CD4(+) T cells did not fill the peripheral naive T cell pool. Injected naive T cells acquired a memory-like phenotype that was stable with time, despite the absence of foreign antigenic stimulation. Their functional capacities were modified, enhanced or abolished depending on the MHC haplotype. Thus, "homeostatic" proliferation of naive CD4(+) T cells in T cell-deprived recipients does not regenerate the naive CD4(+) T cell pool.