All-transretinoic acid inhibited the proliferation of chondrocytes derived from rat xiphoid cartilage when added to the culture medium at 10 −10 −10 −8 M. Proliferation of mouse clonal osteoblastic cells was also inhibited to a significant extent by all-transretinoic acid. However, no such inhibitory effects on rat smooth muscle cells and human fibroblasts were observed. Flow cytometric analyses of chondrocytes labeled with propidium iodide revealed that all-transretinoic acid arrested chondrocytes at the G 1 phase of the cell cycle. Since 9-cisretinoic acid, which is synthesized enzymatically from all-transretinoic acid, also inhibited the proliferation of chondrocytes, we investigated the subtypes of retinoic acid receptors in chondrocytes. Northern blot analysis revealed high levels of mRNA for retinoid X receptor α (RXRα), moderate levels of mRNA for retinoic acid receptor γ (RARγ), and low levels of mRNA for RARα and RXRβ. The mRNA for RARβ and RXRγ were not detected. These results suggest that retinoids are associated with the inhibition of proliferation of chondrocytesviaboth families of nuclear receptors, namely, RARs and RXRs.