Human Hsp27, mouse Hsp25 and αβ-crystallin are part of a diverse family of small heat shock proteins which are produced in all organisms. They function as chaperone-like proteins by binding unfolded polypeptides and preventing uncontrolled protein aggregation. Hsp27 is believed to exist mainly as oligomers of as many as 8-40 Hsp27 protein monomers in cells and data sμggests that the large oligomers of Hsp27 have a chaperone-like activity by serving as a site where unfolding proteins may bind until ATP and Hsp70-dependent refolding can occur. Hsp27 is believed to protect cells by enhancing cellular glutathione levels and elevated glutathione levels have been measured in cells overexpressing Hsp27. Data from studies using wild-type Hsp27 and mutant forms in which the serine phosphorylation sites were mutated to alanines, glycines or aspartates, have shown that cellular glutathione levels depend on the oligomerization of Hsp27. Recent findings indicate that Hsp27 is also a negative regulator of cytochrome c-dependent activation of procaspase-3.