In the research of new bioactive compounds able to regulate the L-arginine metabolism, several substituted amidines were disclosed as potent and selective inhibitors of mainly three enzyme families: the nitric oxide synthase, the dimethylarginine dimethylaminohydrolase and the peptidylarginine deiminase. The present work is focused on the last five years developments in the research for amidine-based inhibitors of the mentioned enzymes and on their potential usefulness in neurodegenerative, inflammatory and autoimmune disorders.