Growth promoting activity for rabbit chondrocytes has been described as a contaminant of partially pruified TSH and LH prepared from bovine and ovine pituitaries. We have investigated fibroblast frowth factor (FGF), a small growth promoting peptide isolated from bovine pituitary tissue, in a rabbit chondrocyte system. The results suggest to us that FGF is the factor or one of the factors responsible for chondrocyte growth stimulating activity previously described in the pituitary hormone preparations. DNA synthesis in these cells is stimulated by FGF at final medium concentrations of 10(-9) g/ml. Bovine NIH-LH is not stimulatory below concentrations of 10(-7) g/ml. FGF also stimulates cell growth in the presence of 10% fetal bovine serum. Dexamethasone, at concentrations of 10(-5) to 10(-9) g/ml exerts a synergistic effect with FGF on both DNA synthesis and cell growth. Over a concentration range of 10(-6) to 10(-9) g/ml, FGF does not stimulate synthesis of sulfated mucopolysaccharides.