The localization of TGF-/J1, -f& and -fQ was studied in the growth plate, epiphysis and metaphysis of the tibiotarsus of three-week-old chicks. The different TGF-/J isoforms were localized to hypertrophic chondrocytes, chondroclasts, osteoblasts and osteoclasts using umnunohistochemical staining analysis with specific TGF-0 antibodies. TGF-^s in osteoclasts and chondroclasts were restricted to those cells located on the respective matrices. TGF-/33 localization was mainly cytoplasmic in the transitional (early hypertrophic) chondrocytes, but nuclear staining was also detected in some proliferating chondrocytes. The cell-specific localization of these TGF-/J isoforms supports the hypothesis that TGF-/J has a role in the coupling of new bone formation to bone and cartilage matrix resorption during osteochondral development and suggests that TGF-/S may be a marker of chondrocyte differentiation. TGF-/J localization preceded a marked increase in type II collagen rnRNA expression in transitional chondrocytes, suggesting a role for TGF-/J in the induction of synthesis of extracellular matrix.