The heat shock proteins (HSPs) are believed to act as molecular chaperones which appear to play some roles in regulation of normal protein folding and also in preventing damage to protein structures under various conditions of environmental stress. We examined the expression of the major HSP families, HSP60, 70 and 90 families and small HSP32, at the mRNA level in ocular development. Expression of HSP32, HSP60, HSP70, HSP84, HSP86 and heat shock cognate protein (HSC)70 mRNAs was examined by in situ hybridization. HSC70, HSP84, HSP86 and HSP60 mRNAs were expressed strongly in all ocular tissues during early stages 3 to 5, corresponding to embryonic day (E)11.5 to E14.5. At stages 6 to 7 (E15.5 to E18.5), the expression of these four mRNA species was decreased markedly in most ocular tissue, while in the retina strong HSC70 and HSP86 mRNA expression was still detected. HSP32 and HSP70 mRNAs were not detected at any stage. These results suggest that the expression of HSPs is developmentally regulated through ocular organogenesis, and the proteins may play some important roles in ocular development.