In view of the need to exploit saline water resources in agriculture in arid zones, we investigated the salt tolerance of Opuntia ficus-indica in plants growing in solution culture. Salt (NaCl) was added in concentrations ranging from 5 (control) to 200 mol m-3. Cladode growth was sensitive to salinity, being 60% of the control at 50 mol m-3 NaCl. The root-to-stem ratio decreased significantly only at 200 mol m-3. Various other parameters were studied, such as water content, Na, K and Cl content, osmotic pressure, and CO2 uptake. Of these parameters the decreases in cladode water content and CO2 uptake were related to the decrease in cladode growth. Raised salinity increased cladode osmotic pressure, which was associated with tissue dehydration. We concluded that osmotic adjustment does not occur in prickly pear under salt stress.