L-Homoarginine is a cationic amino acid derivative, which is structurally related to L-arginine and lysine. Several lines of evidence point to nervous tissue as an important target of homoarginine action. In the mammalian brain homoarginine can be detected in noticeable quantities, but its origin is currently poorly explored. In part I of this review we try to show that both uptake and transport into brain (carried out by cationic amino acid transporters) and local synthesis in the brain (carried out by the homoarginine-synthesizing enzymes L-arginine:glycine amidinotransferase and ornithine transcarbamylse) might contribute to homoarginine brain content. We then give a brief overview about the multiple effects of homoarginine on the healthy brain and show that both homoarginine excess and deficiency are potentially harmful to the central nervous system. In part II, we shortly report about own experiments with regard to the cellular localization of cationic amino acid transporters, as well the enzymes L-arginine:glycine amidinotransferase and ornithine transcarbamylse, in human and rat brains.