Biological homeostasis is maintained by protective mechanisms, involving local reactions in the injured tissue and whole body reactions. Overexpression of the protective mechanisms is, however, sometimes injurious to the organism. The Symposia on Cytoprotection are held annually to discuss cytoprotective mechanisms from both basic and clinical viewpoints. The topics of the presentations vary widely, from gastrointestinal mucosal disturbances, liver and pancreatic dysfunctions, cerebral ischemia, endothelial cell function to biochemical characteristics of cancer cells, and tissue damage produced by excessive production of superoxides and free radicals and protective procedures for such damage. In one of the two Special Lectures, Professor Kyoko Hotta reviewed recent results of biochemical studies of mucus glycoprotein and the relations between the protective functions and the structural properties of mucus. Professor Shin-ichi Akiyama reported that multi-drug resistance is due to drug efflux resulting from a 170 kD membrane glycoprotein (P glycoprotein) and that agents that reverse multidrug resistance do so by competing with cytotoxic drugs for a binding site on P glycoprotein, the drug efflux pump. The concept of cytoprotection should be applied to protective mechanisms against various stresses in organisms. The results reported in this Proceedings will contribute to the further development of biochemical physiological research. Original reports are published as full papers. Papers that have appeared or will appear in other publications are published here as summaries.