The present invention provides new salts and/or addition compounds and/or complex compounds of guanidinoacetic acid with malic acid, aspartic acid, ascorbic acid, succinic acid, pyruvic acid, fumaric acid, gluconic acid, α-ketoglutaric acid, oxalic acid, pyroglutamic acid, 3-nicotinic acid, lactic acid, citric acid, maleic acid, sulfuric acid, acetic acid, formic acid, 2-hydroxybenzoic acid, L-carnitine, acetyl-L-carnitine, taurine, betaine, choline, methionine and lipoic acid as well as in the form of sodium, potassium or calcium guanidinoacetate. These salts have improved physiological and therapeutic properties and are particularly suitable for use as dietary supplements, as animal feeds and in cosmetic or dermatological preparations in which especially the marked stability and good bioavailability of the salts come to the fore.