Two NAD: arginine ADP-ribosyltransferases (transferase "A" and "B") were identified in turkey erythrocytes and purified to homogeneity. Both transferases in the presence of NAD catalyzed the ADP-ribosylation of arginine, other low molecular weight guanidino compounds and proteins. ADP-ribosyltransferase A was activated by chaotropic salt or histone. Activation was associated with the disaggregation of an inactive, rapidly sedimenting, high molecular weight species to a protomeric form of approximately 28,000 daltons; this protomer in equilibrium aggregate transition was rapidly reversible. In the presence of salt, the Km's for NAD and arginine methyl ester were 15 microM and 1.3 mM, respectively; the turnover number for the purified enzyme was approximately 9,900 mol X min-1 X mol enzyme-1. ADP-ribosyltransferase B exhibited a substrate specificity clearly distinct from that of transferase A. Transferase B had a Mr of 32,000, slightly larger than that of the transferase A protomer. The activity of transferase B was unaffected by histone and inhibited by chaotropic salts; its Km's for NAD and arginine methyl ester of 36 microM and 3 mM, respectively, were similar to those obtained with transferase A. These studies are consistent with the presence of two different NAD: arginine ADP-ribosyltransferases in turkey erythrocytes exhibiting distinct kinetic, regulatory, and physical properties.