Several species of scavenger receptors have so far been identified. However, it remains unclear which receptors are more crucial for the foam cell formation and progression. In the present study, we compared five major scavenger receptors (SR-A, CD36, CLA-1, CD68, and LOX-1) in their levels of expression at the different stages of foam cells derived from THP-1 cells. The expression of all scavenger receptors examined was up-regulated by the stimulation with TPA for 48 hours, despite the expressions of SR-A, CD36 and LOX-1 being very low before the treatment with TPA. Four to 7 days after the removal of TPA, the levels of CD36, CLA-1 and CD68 were increased significantly. In contrast, the expression of SR-A was suppressed significantly, and no change was observed in that of LOX-1. Furthermore, when the transformed macrophages were incubated with oxidized LDL, in which the uptake of [3H] cholesteryl oleoyl ether-labeled OxLDL was linear up to 7 days after the addition of OxLDL, the expression of CD36, CLA-1 and CD68 were greatly enhanced. This enhancement was more prominent than that without oxidized LDL, and the enhancement was sustained throughout the experimental period. On the other hand, SR-A was not up-regulated, and LOX-1 was down-regulated. We thus propose that CD36, CLA-1 and CD68, but not SR-A and LOX-1, may play crucial roles in the progression of macrophages to foam cells, which is a key step for the initiation of atherosclerosis.