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During endochondral bone formation, as occurs in fracture healing, chonclrocytes arc one of the first cells to see an implant surface. We tested the hypothesis that chemical composition and surface roughness affect chondrocyte differentiation, matrix synthesis, and local factor production and that the nature of the response is dependent on the statc ol maturation of the cells. To do this, we harvested rat growth zone and resting zone chondrocytcs and examined their response to smooth and rough disk surfaces manufactured from either commercially purc titanium or titanium alloy. Profilometry scanning electron microscopy. Auger spectroscopy, and Fourier transform infrared spectroscopy were used to characterize the surfaces. Average roughness values were 0.22 pm for smooth titanium surfaces, 0.23 pin for smooth titanium alloy surfaces. 4.24 pm for rough titanium surfaces, and 3.20 pm for rough titanium alloy surfaces. Cells were grown on the different disk surfaces until the cultures had reached confluence on plastic. The effect of the surfaces was determined by assaying cell number and [3H]thymidine incorporation as measures of cell proliferation. cell layer and cell alkaline phosphatase specilic activity as markers of differentiation, and collagen production and (3'S]sulfate incorporation as indicators of extracellular matrix production. In addition, the synthesis of prostaglandin E, and transforming growth factor-B were examined to measure changes in local factor synthesis. In growth 7one and resting zone cultures, cell number and ["Hjthymidine incorporation were decreased on rough surfaces; however, this effect was greater on commercially purc titanium surfaces. Cell layer and cell alkaline phosphatase specific activity were decreased in resting zone cclls grown on rough surfaces. Cell alkaline phosphatase specific activity in growth zone cells was decreased on rough surfaces, whereas cell layer alkaline phosphatase specific activity was increased only in growth zone cells grown on rough commercially pure titanium surfaces. Resting zone cell collagen production was decreased only on rough commercially pure titanium. whereas in growth zone cells, collagen production was increased. Increased prostaglandin E2 release into the media was found for growth zone and resting zone cell culturcs on the disks with rough surfaces. The observed effect was greater on rough commercially pure titanium. Production of transforming growth factor-p by resting zones was similarly affected, whereas an increase in its production by growth zone cells was measured only on rough commercially pure titanium. These results indicate that surface roughness affects chondrocyte proliferation, differentiation. matrix synthesis, and local factor production and that these parameters are also affected by chcmical composition. Furthermore. the nature and cxtcnt of the cell response is dependent on cell maturation. The overriding variable in response to an implant material, however, appears to be roughness of thc surface.