Abstract: The effect of Gd(Ⅲ) on Ca(Ⅱ) species in human interstitial fluid was studied by mathematical model method. Meantime artificial neural network was applied to the estimation of lg β value of some complex. The results show that the variety of concentration of Gd(Ⅲ) has effect on Ca(Ⅱ) species. At the background the concentration of Gd(Ⅲ) in human interstitial fluid, Ca ²⁺ (71.0%), [Ca(HCO₃)](9.5 %) and (6.0%) are main species. With the concentration of Gd(Ⅲ) rising, Gd(Ⅲ) firstly competes with Ca(Ⅱ) for PO₄^3- and CO₃^2-, then tends to compete for other biological low molecular weight ligands. This leads to Ca(Ⅱ) redistribution with the variety of concentration of Gd(Ⅲ).

Key words: Human interstitial fluid, Gd(Ⅲ), Ca(Ⅱ), Mathematical model method, Artificial neural network