<p><b>OBJECTIVE</b>To study the effect of platelet-derived growth factor-BB (PDGF-BB) in different concentrations on proliferation of tendoncells cultured in vitro.</p><p><b>METHODS</b>Rattendoncells were cultured and identified in vitro. The rattendoncells were cultured in PDGF-BBnutrientsolution in different concentrations. They were then divided into 1, 5, 10, 20, 50, 100, 150, 200, 250 ng/mL PDGF-BB groups (cultured with 0.1 mL 0.5% PBS with addition of 1, 5, 10, 20, 50, 100, 150, 200, 250 ng/mL PDGF-BB respectively). Tendoncells in control group were cultured with 0.1 mL 0.5% FBS. Proliferation of tendoncells was detected by MTT test. The absorbance values of tendoncells in control group and 20 ng/mL PDGF-BB group before culture and after cultured for 12, 24, 36, 48, 60, 72 hs were determined.</p><p><b>RESULTS</b>The isolated cells were identified to be rattendoncells as they were Type I collagenstaining positive and TypeIII collagenstaining negative. Compared with that of control group, the absorbance values of other groups were all increased, except for that of 250 ng/mL PDGF-BB group (P < 0.05 or P < 0.01). Besides, the absorbance value rose gradually with the increase of the concentration of PDGF-BB on, and then diminished gradually with the increase of the concentration of PDGF-BB from 20 ng/mL on. Tendoncells in 20 ng/ml PDGF-BB group began to increase in number when cultured for 12 hs, and it reached the highest level (0.53 +/- 0.04) at 48 h, which were obviously higher than those of control group at 24 - 72 h (P < 0.01). The absorbance value of tendoncells in 20 ng/mL PDGF-BB group was significantly higher than that of control group at 24, 36, 48, 60, 72 h after culture (P < 0.01).</p><p><b>CONCLUSIONS</b>PDGF-BB can promote the proliferation of tendoncells in a definite range of concentration and time.</p>