The interactive effects of salinity and potassium deficiency on the growth, mineral elements and photosynthetic performance were investigated in wild (Hordeum maritimum L.) and cultivated barley (Hordeum vulgare L. var. Manel). At 28 d of growth, plants were treated with 3 mM K and 0 mM NaCl (3-0); 3 mM K and 100 mM NaCl (3-100); 0 mM K and 0 mM NaCl (0-0), 0 mM K and 100 mM NaCl (0-100) for 14 d. In both species, biomass production decreased considerably when the two constraints were applied simultaneously. Salinity affected shoots more than roots, whereas for potassium deficiency, the reverse occurred. Generally, potassium uptake was more affected in wild than in cultivated barley and, independent of potassium availability, 100 mM NaCl increased Na+ content in both species, whereas K+ deprivation increased Na(+) content only in H. maritimum shoots (0-0). Potassium-use efficiency (KUE) increased in all treated plants. Potassium deficiency increased the negative effects induced by salt in the photosynthetic process of H. vulgare, and this species seemed to be unable to counteract the negative effects of salinity. H. maritimum showed limitation in CO2 photoassimilation, but this species displayed mechanisms that play a role in avoiding PSII photodamage aimed to dissipate the excess energy.