Objective To investigate the effects in vitro of 17 β-estradiol (E2) on the proliferation and metabolism otrabbit mandibular condylar cartilage cells Methods Chondrocytes were derived from neonatal rabbit mandibular condylar cartilage using a modified enzyme method 17 β-estradiol was added to the culture medium in a variety of concentrations Cell growth and DNA, collagent and proteoglycan synthesis were used as indicatms of pregferation and differentiation of condylar chondrocytes. These were measured by cell number. H-proline and S-incorporation. respectively Results E2 increased cell number and H-thymidine incorporation at 10mol/L, and 10 0.10mol/L in a dose-dependent manner. peaking at 10mol/L and 10mol/L. respectively However, further lncrease in the concentration of estradiof caused inhibition of both cell number and H-thymidine incorporation, and this was significant at 10mol/L The effect of E2 on proteglycan synthesiswas similar; the maximum stimulating effect was at 10mol/L. and inhibition was significant at 10mol/L There was no obvious stimutatory effect of E2 on H-tbymidne incorporation observed Conclusions Estradiol affects condylar chondrocyte cell growth, DNA and proteoglycan synthesis in a biphasic manner depending on its concentration. This indicates that estrogen may be important in the probferalion and differentiation of mandibular condylar chondrocytes, and could be relevant to some aspects of certain tempormandibular joint diseases by madulating the function of the chondrocytesv