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In desert areas, salts are known to accumulate in surface layers. Among the highly soluble salts. nitrate is the least studied. In the Zin area of the Negev Desert (southern Israel), the Quaternary veneer and the underlying phosphorite-bearing formation are characterized by high concentrations of soluble nitrate, chloride and sulphate. The heavy pollution of groundwater by these components is caused by the dressing of phosphorite ores mined in the area. Nitrate deposits discovered in Pleistocene and underlying Cretaceous formations of the Negev, reflect climatic changes from humid to dry conditions that prevailed during the Pleistocene. During the humid periods, soils were formed and soluble salts which had previously permeated the sediments, were flushed out. With onset of desertification of the Negev, nitrate was released from oxidized organic matter in the soil and accumulated in the sediments together with exogenous chlorides and sulphates.