Protonation constants and Mg2+-, Ca2+-, Pb2+-, Mn2+-, Co2+-, Ni2+-, Cu2+-, Zn2+- and Cd2+-glycine complex formation constants have been determined in different aqueous media at different temperatures. Salt effects are explained by a complex formation model which takes into account the formation of weak species. From the temperature dependence of the formation constants, thermodynamic parameters Delta H-Kelvin (and in some cases Delta C-p(Kelvin)) have been obtained. A rigorous analysis of literature data, together with experimental findings, allows recommended formation parameters, in the ranges 0 less than or equal to I-e less than or equal to 1 mol l(-1) (I-e is the effective ionic strength) and 5 degrees C less than or equal to T less than or equal to 45 degrees C, to be obtained. Because the proposed model can be used in any electrolyte mixture in the above I and T ranges, the speciation in seawater, and other natural fluids, can be simulated by appropriate computer programs. The validity of the present approach which takes into account the ionic strength dependence of formation constants, together with the concepts of effective ionic strength and complex formation model, is discussed.