Heat shock proteins are ubiquitous proteins and have been characterized as cytoprotective molecular chaperones. The typical function of a chaperone is to assist a protein to attain its functional conformation to prevent non-functional aggregation of misfolded proteins. The principal HSP families are HSP90, HSP70, HSP60 and the small HSPs including HSP27, ubiquitin, α-crystallin, Hsp20 and others. The common functions of small Hsps are chaperone activity, thermotolerance, inhibition of apoptosis, regulation of cell development, and cell differentiation. Hsp27 has a molecular weight of approximately 27 kDa, although it has been shown to form large aggregates of up to 800 kDa in the cytosol. Hsp27 is found in several types of human cells, including tumour cells. Hsp27 interferes with apoptosis through its ability to interact with and inhibit key components of the apoptotic signaling pathway, including the caspase activation complex. Overexpression of heat shock proteins can increase the tumorigenic potential of tumour cells. HSP27 also has been reported to be involved in development and progression of hormone-refractory prostate cancer. Involved in stress resistance and actin organization.