Atherosclerosis is an inflammatory disease. T lymphocytes, occurring concomitantly with macrophages, are found in atherosclerotic lesions with substantial numbers in all stages. Most of the T cells in the lesions are CD4(+) T cells. The finding of activated T cells and macrophages in lesions and cloning of T cells specific for modified low-density lipoproteins from lesions suggest that a cell-mediated immune reaction is taking place in atherosclerosis. This review provides an overview of our current understanding of the roles of CD4(+) T cell subpopulations in atherosclerosis.