Waters of the eastern Mediterranean portray an unusual pattern of stable isotope composition compared with other evaporitic systems: an increase in O-18 concentration up to value of delta(18)O = +2.2 parts per thousand is not matched by a commensurate increase of deuterium. It is shown that this unusual pattern is an expression of the ''medi-terranean'' location of the sea, where the air-sea interaction with relatively dry and isotopically depleted continental air masses dominates the evaporation process in winter and where the diluting meteoric waters are extremely depleted in the heavy isotopes. As a result, the slope of the evaporation line in delta(H-2)-delta(O-18) space is lower than in other marine systems, whereas the mixing line between the meteoric waters and the seawater is very steep. This pattern provides an independent method for the estimation of the evaporation E and freshwater influx terms M of the water balance of the Mediterranean Sea. In winter the ratio of evaporation to freshwater input is found to be E/M = 1.20, whereas in summer this ratio E/M = 1.83.