In this book, the authors present current research in the study of the structure, biology and clinical significance of calpain, enzymes and enzyme activity. Topics discussed include monitoring the activation of calpain I for sensitive assessment of pathogenesis and neuroprotectant action; the myeloperoxidase enzyme as a diagnostic biomarker and target for new drug developments; the biological effects of calpain inhibitors on human phagocyte functions; ALDH activity of Artemia as a tool for the investigation of the toxicity of antifouling paints; and calpain as an indicator of organophosphorous-induced delayed neuropathy.