The 47-kDa heat shock protein (HSP47) is assumed to be a molecular chaperone specific to collagen. We examined and compared the expression patterns of HSP47 and alpha 1(I) collagen in the developing mouse cornea. Expression of HSP47 and alpha 1(I) collagen mRNAs was assessed by Northern blot analysis and in situ hybridization, and that of HSP47 protein was determined by Western immunoblotting and immunohistochemistry. HSP47 mRNA and protein were expressed strongly in early embryonic ocular tissues and were developmentally down-regulated during ocular development. Both were distributed in the mesenchymal cells (presumptive corneal stroma, sclera and choroid) and hyaloid blood vessels until post-natal day 14. The level of alpha 1(I) collagen mRNA increased during ocular development, was maximally expressed in the three days after birth, and was detected in mesenchymal cells. HSP47 expression is regulated developmentally toward completion and plays an important role during ocular development especially in corneal morphogenesis. We discuss here the relation between expression of HSP47 and alpha 1(I) collagen.