Tomato ( Lycopersicon esculentum Mill. cv. Pera) calli tolerant to 50 mM NaCl were obtained by successive subcultures in NaCl supplemented medium. Salt-tolerant calli showed an increase of fresh and dry weight respective to control calli. When control and 50 mM NaCl-tolerant calli were stressed with 100 mM NaCl for 48 h, a decrease in respiration rate of 32 and 9%, respectively, was observed. Relative proportions of phospholipid fatty acids and free-sterol molecular species were the same in both control and NaCl tolerant calli. While the content of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) increased in salt-tolerant calli, the free sterol content was similar in both cases. A substantial increase of vanadate-sensitive ATP-dependent H + pumping activity without any modification in specific phosphohydrolytic activity and in passive H + conductance was detected in microsomes from salt-tolerant calli, which could be explained by an increased coupling between H + pumping and ATP hydrolysis. The higher lipoxygenase and antioxidant enzyme activities such as superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase and glutathione- S-transferase in 50 mM NaCl-tolerant calli as compared to controls also suggest that salt-tolerant calli has a high capacity of polyunsaturated fatty acid hydroperoxide formation and active oxygen species scavenging.