A recent immunoelectron microscopic study of type X collagen in developing cartilage gave results that could be explained by movement of the molecule from one region of the cartilage matrix to another, there becoming associated with preexisting collagen fibrils. In the present study, to test the feasibility of this model we incubated pieces of nonhypertrophic, embryonic chicken sternal cartilage (which has no endogenous type X collagen) in medium with type X collagen and then used immunofluorescence and immunoelectron microscopy to evaluate movement of the molecule through the matrix. The results show that type X collagen molecules can indeed pass through embryonic sternal cartilage matrix and subsequently become fibril-associated.