The proinflammatory cytokine interleukin (IL)-1β and the IL-1 receptor antagonist are expressed by atherosclerotic plaques and may be linked to the development of atherosclerosis. Existing evidence shows that retinoids and their receptors are involved in inflammatory response and that they are found in atherosclerotic plaques. In all- trans-retinoic acid (atRA)-treated human aortic smooth muscle cells (AOSMC), significant increases in IL-1β levels were observed, compared with untreated cells. Examination of IL-1 receptor antagonist and IL-1 receptor type I levels did not show any difference between atRA-treated and -untreated AOSMC. The results show that atRA-treated AOSMC express both the precursor (33 kDa) and the active form (17 kDa) of the IL-1β protein. atRA-treated carotid lesions showed significantly elevated IL-1β mRNA levels (2.9 ± 2.33) compared with untreated lesions (2.0 ± 1.77; p < 0.05). These results support the role of atRA as a regulator of inflammation such as in atherosclerosis.