Atherosclerosis involves inflammatory processes between vascular tissues and hematocytes with a hyperlipidemic background. To examine whether variations of hematocytes constitute one of the genetic components in atherosclerosis, irradiated apolipoprotein E (apoE)-deficient (apoE(-/-)) mice with hypercholesterolemia and preexisting atherosclerotic lesions were reconstituted with mixed bone marrow cells (BMC) from syngeneic and wild-type (apoE(+/+); atherosclerosis-resistant SJL or -susceptible B10.S) mice. Stable mixed allogeneic chimeras with small amounts of serum apoE were established without any detrimental complications. Compared with untreated apoE(-/-) mice or apoE(-/-) mice transplanted with syngeneic BMC alone, significant reduction of the cholesterol level and significant lesion regression were observed in the mixed chimeras. Furthermore, mixed chimeras given SJL BMC showed marked reductions in numbers of lesions compared with those reconstituted with B10.S BMC. Cholesterol levels in the former SJL chimeras, however, were significantly higher than those in the latter B10.S chimeras. These findings indicate that the resistance of SJL to atherosclerosis resides in the bone marrow-derived cells.