Salinity-calcium interactions, which have been shown to be important in plants grown in dryland saline soils of the Farm of Agricultural Research Station, Sabahia, Alexandria, were studied in two species differing in salt tolerance.  In solution culture, wheat showed a greater reduction in growth and a higher incidence of foliar Ca deficiency symptoms than barley when grown under MgSO₄ or Na₂SO₄ plus MgSO₄ salt stress.  Amendment of the saline solution with Ca to increase the Ca/(Na+Mg) ratio ameliorated the effects of salt, but more so in wheat than in barley.  At least part of the difference in salt tolerance between the two species must therefore relate to species differences in the interaction of salinity and Ca nutrition.  The greater response of wheat to Ca was not due to a lower Ca status in leaf tissue; on the contrary, although Ca amendments improved tissue Ca/(Na+Mg) ratios in both species, salinized wheat had equivalent or higher calcium content, and higher Ca/(Na+Mg) ratios than did barley.  The higher calcium requirement of wheat is apparently specific to a saline situation; at low salinity, wheat growth was not reduced as extensively as that of barley as Ca/(Na+Mg) ratio was decreased.  High night-time humidity dramatically improved wheat growth under saline conditions, but increasing the calcium concentration of the saline solution had no effect on growth in the high humidity treatment.  Membrane leakage from leaf tissue of wheat grown under saline conditions was increased compared to tissue from non-saline plants.  Plants grown in Ca-amended saline solutions showed no increase in membrane leakage.  These results confirm the importance of calcium interaction with salinity stress, and indicate difference in species response.