ABSTRACT This study was conducted through 1996-1999 years in the Department of Pomology, Faculty of Agriculture, Alexandria University. The work involved the evaluation and selection of salt tolerant callus of sour orange under in vitro conditions. The main results can be summarized in the following points: 1-Concerning the effect of exposure to different concentrations of NaCl salt in culture medium on callus survival percentage, the results indicated that  the 10gl^-1 NaCl concentration was lethal for most callus with only 20.00% surviving. 2- Regarding the effect of exposure to different concentrations of NaCl salt in culture medium on ion content percentage (on dry weight basis) of salt-sensitive and salt-tolerant calluses of sour orange, the results revealed that at 5gl^-1 NaCl concentration, the NaCl –tolerant callus had higher K⁺ content, as compared with the NaCl-sensitive callus. On the contrary, the NaCl-tolerant callus had lower Cl^-, Ca²⁺ and Mg²⁺ contents, as compared with NaCl-sensitive callus, at the same external NaCl concentration (5gl^-1 NaCl). 3-The obtained results also revealed that proline content increased in salt-tolerant callus as compared to salt-sensitive callus (control). Accumulation of proline in the salt-tolerant callus has been shown to be an adaptive mechanism for resistance to salt stress.