Heat shock proteins (HSPs) have been identified in all cells, prokaryotic and eukaryotic, to protect the cells from harmful insults and stress. Increased HSP synthesis can also result during normal cellular functions and also respond to exposure from environmental stress and infection. Although the molecular mechanisms responsible for HSP cellular protection are still not fully understood, their expression is critical for cellular survival and can be modified by cell signal transducers such as intracellular pH, cyclic AMP, Ca2+ Na+, inositol [correction of inostitol] triphosphate, protein kinase C, and protein phosphates. Most HSPs interact, assemble, fold, unfold, bind, transport, translocate and 'chaperone' other proteins in the cell and alter their function.