The solubility of Fe, Mn, Cu and Zn in calcareous soils was determined by modified DTPA equilibrium method which enables the simultaneous measurement of the solubility of the micronutrient cations. Soluble hydroxy ions of Fe increased the total metal ion activity several fold over Fe3+ activity in equilibrium with ferric oxides and hydroxides. The hydroxy ions of Cu and Zn could enhance their net activity up to the extent of 10-100 times over the Cu2+ and Zn2+ activities in soil solution. A concept of Fe ion buffer system likely to regulate the activities of Fe3+ ionic species is proposed. Complexing of metal ions by natural organic ligands seems to exert a profound influence on their pH dependent solubility as is evident from a significant correlation between the activities of these metal ions and organic C content of thes soils.