The binary and ternary systems of cobalt(II) and nickel(II) with the aminoacids glycine, serine, aspartic acid and guanidinoacetic acid were studied. Theamino acids glycine - Gly, serine - Ser, aspartic acid - Asp and guanidinoaceticacid - Gaa are all involved in several biochemical processes. These amino acidsare constituents of many proteins, which are in turn, good complexing agents. Thestudy of metal-amino acid interactions are of great interest, as they representsimplified models for the analysis of the changes caused in the proteins properties, when these bond to metal ions. It was determined, in this work, theformation and interaction constants of species belonging to the binary and ternarysystems of cobalt(II) and nickel(II). UV-Vis spectrophotometric analysis werealso made for each of the systems studied. The comparison of the UV-Vis spectrain different pHs with the species` distribution graphs indicated a relationshipbetween the d-d bands and the respective proposed specie. When analyzing theformation constants of the ternary complexes ML1L2, the Ni(II) complexesshowed higher values than those of respective Co(II) complexes, a pattern whichis in accordance with the Irving-Williams series. In conclusion to the comparisonof the UV-Vis spectra with those in literature, we have that the bands found, aswell as their respective position and molar absortivities, refer themselves to nonregularoctahedral complexes. It was verified that the greatest intramolecularinteractions beetween the ligands in the complexes studied were those of thespecies cointaining Gaa. From the graphs of species distribution in terms of pH, we were able to verify that in biological pH, for all three systems of Co(II),protonated ternary species were predominant. No generalizations were visible forthe Ni(II) systems. In the Ni Gly Ser system, the specie NiGlySer is present ingreater amounts in pH close to 7; in the Ni-Asp-Gly system, the ternary speciesare formed in lower quantities in lower pH values and in higher and biological pHvalues, binary species of hydrolyzed NiAsp are predominant; in Ni-Ser-Gaasystems, protonated ternary species are in higher concentration. In pH 9,hydrolyzed (binary and/or ternary) species were found in all ternary systems. Inmore basic medium, the ternary species were fragmented, therefore generating ML(OH)3 and ML(OH)4 hydrolyzed binary species, which have in turn greaterstability.