Temary complex systems M(II): salicylic acid derivatives (as primary ligands): acidic and Basic amino acids (as secondary ligands) have been investigated by the potentiometric technique. Formation constant values of the various binary and temary complexes liable to exist in such systems have been determined at 25 °C and p. — 0.2 mol dm-3 KC1. The order of stability of the binary or temary complexes in tcrms of nature of metal ion, salicylic acid derivative and amino acid as well as the stability of the ternary complex compared to that of the binary amino acid complex are examined and discussed.