The annual killifish Austrofundulus limnaeus inhabits ephemeral ponds in regions of northern South America, where they survive the periodic drying of their habitat as diapausing embryos. These diapausing embryos are highly resistant to a number of environmental insults such as high temperature, dehydration, anoxia, and increased salinity. Molecular chaperones are known to play a role in stabilizing protein structure and function during events of cellular stress. Relative levels of heat shock protein (Hsp)70 were measured in developing and diapausing embryos of A. limnaeus using quantitative Western blots. An inducible or embryo-specific form of Hsp70 is expressed during embryonic development in A. limnaeus and is elevated during diapause II in this species. Constitutive expression of Hsp70 during development may afford these embryos protection from environmental stresses during development more quickly than relying on the induction of a classic heat shock response.