Cotton (Gossypium hirsutum) was assessed for its acclimation potential to heat, chilling, and salinity stress. Pretreatment at 40°C for 6 days reduced the extent of decrease in CO2 assimilation on exposure to 49°C. This was associated with an increase in transpiration relative to the experimental control level, which did not occur in control-pretreated plants. The acclimating heat-pretreatment induced an increase in transpiration, as determined on the final day of treatment, and an increase in stomatal conductance on subsequent return to control temperature. This indicated an increase in plant hydraulic conductance, suggesting the involvement of transpirational cooling in the observed phenomenon of heat acclimation. Pretreatment at lo w temperatures decreasing gradually from 18 to i 3°C by 1 °C per day followed by recovery in control temperature for 1 day reduced the extent of chronic photoinhibition during subsequent treatment at 11 °C under moderate incident light. This was associated with a reduced extent of leaf death in response to treatment at 11 °C. The low temperature pretreatment induced photosynthetic responses of predominantly acclimative nature, as indicated by photo-protective photoinhibitory quenching and a slight increase in net rate of CO2 uptake following the initial decline. Subsequent recovery in control temperature for 1 day induced an increase in Fm, suggesting increased yield of electron transport through photosystem II. The same chilling pre-treatment partially protected photosynthetic processes on exposure to 49°C, as indicated by a reduced extent of decrease in maximum quantum yield of PSII and net rate of CO2 uptake. Pretreatment at 120 mo! m-3 NaCl reduced the extent of increase in leaf sap Na+ concentration on exposure to 300 mo! m-3 NaCl. Increased leaf succulence explained part of this phenomenon, whereas the reduced extent of increase in leaf Na+ concentration on a dry weight basis suggested the involvement also of other mechanisms of control of leaf Na+ concentrations.