To verify the role of certain biochemical substances such as proline in regulating the biochemical activity of citrus fruits, calli of citrus aurantium were grown under Murashig and tucker (MT) culture media containing 3, 6, 8, 9 g.l^-1 of NaCl and 0.5, 25, 50 mg/l of proline. Results showed that addition of exogenous proline to the culture medium neutralized the inhibitory effects of NaCl and increased the induction and growth rate of the calli, particularly at high NaCl levels. These results suggest the potential role of proline in protecting these fruit species, such as Citrus aurantium, under abiotic stress.