The ability of two strains of Azospirillum brasilense to mitigate NaCl stress in barley plants was evaluated. Barley seedlings were inoculated and subjected to 200 mM NaCl for 18 days. Several days after NaCl treatment, a significant decline in biomass as well as in height was observed in uninoculated plants. However, smaller reductions in biomass and height were detected in plants inoculated with strain Az39. All the stressed plants showed significantly higher Na+ but lower K+ contents in their shoots. The growth rate of uninoculated plants was adversely affected by saline treatment, which was associated with higher putrescine content and lower levels of HvPIP2; 1 transcripts in the roots. Azospirillum inoculation triggered the transcription of this gene. Our results suggest that barley plants inoculated with A. brasilense may be better prepared to thrive under saline conditions. To our knowledge, this is the first report showing an effect of Azospirillum inoculation on the expression of PIP2; 1, a gene involved in the synthesis of root water channels.