Enzymes have been identified in animal tissues that catalyze the mono(ADP-ribosyl)ation of arginine and proteins. Since these NAD:arginine ADP-ribosyltransferases under physiological conditions do not appear to catalyze the degradation of the product ADP-ribose-arginine, the possibility was investigated that a different family of enzymes exists that cleaves the ADP-ribose-arginine linkage. An enzyme was identified in and partially purified from turkey erythrocytes that catalyzed the degradation of ADP-ribose-[14C]arginine synthesized by a salt-activated NAD:arginine ADP-ribosyl-transferase, resulting in the release of a radiolabeled compound that was characterized chromatographically and by amino acid analysis as arginine. This putative arginine product was converted in a reaction dependent on NAD and the NAD:arginine ADP-ribosyltransferase to a compound exhibiting properties characteristic of ADP-ribose-arginine. Action of cleavage enzyme on [adenine-U-14C]ADP-ribose-arginine resulted in the release of a radiolabeled compound that behaved chromatographically like [adenine-U-14C]ADP-ribose. Since degradation of ADP-ribose-arginine appears to generate an arginine moiety that is a substrate for the NAD:arginine ADP-ribosyltransferase, it appears that ADP-ribosylation may be a reversible modification of proteins.