<p>Expression of collagen type III and tenascin-C was investigated in developing joints of embryonic chick skull using immunohistochemistry and in situ hybridization. At E8.0, the quadratomandibular joint was formed between the quadrate cartilage and the articular cartilage, with an intervening interzone consisting of fibrous tissues. Collagen type III immunoreactivity and <i>COL3A1</i> mRNA expression were restricted to the interzone and the surface layer of cartilage. By contrast, tenascin-C expression was detected throughout the peripheral layer of the cartilage, but the expression intensity was reduced in the surface layer within the joint, indicating that both molecules exhibit a distinctive expression pattern. This expression pattern was maintained at E15.0, after formation of the articular space. At E11.0, the quadratosquamosal joint was formed between the quadrate cartilage and squamosal bone, with the perichondrium and periosteum intervening. Collagen type III expression was restricted to the perichondrium within the joint. Meanwhile, tenascin-C expression was detected throughout the perichondrium and peripheral layer of the cartilage, but the expression intensity was reduced within the joint, indicating a distictive expression pattern similar to that of quadratomandibular joint. At E14.0, the pterygoid-parasphenoid joint was formed between the palatoquadrate cartilage and parasphenoid cartilaginous pad, with a narrow interzone. Immunoreactivity indicative of collagen type III and tenascin-C expression was observed throughout the cartilage area, with regional differences in staining intensity, which also suggests a distinctive expression pattern. These results suggest that both collagen type III and tenascin-C may be associated with joint formation in chick skull.</p>