This investigation was conducted in the form of five separate experiments to evaluate the effects of salinity and some stress modulators on the physiological and biochemical characteristics of sorghum plants. The first study included a Petri dish experiment conducted in a growth chamber to investigate the response of six cultivars (Pegah, Speed feed, Jumbo, Kimia, Sepideh and Payam) and four lines (GS4, KGS29, KGS23, MGS5) of sorghum to four salt levels (0, 100, 150 and 200 mM NaCl) at germination and early seedling stage. Results showed that salinity decreased germination percentage, germination index, seed vigor, shoot and root length and fresh and dry weights but increased mean germination time of all tested genotypes. Considerable variation was observed in this experiment among sorghum genotypes in terms of the response to salinity. The second study included a field experiment designed to evaluate the response of the ten sorghum genotypes used in the germination test to three salinity levels (control, 60 and 120 mM NaCl). This experiment was a 3-replicated split-plot arranged in a randomized complete block design in which salt treatments were accommodated in main plots and the tested genotypes were placed in sub-plots. In this field experiment salinity reduced photosynthetic rate, stomatal conductance, intercellular CO2 concentration, leaf area index, leaf relative water content, chlorophyll a, b and carotenoids concentrations, membrane stability index, silage dry matter and fresh and dry forage yield, but increased the concentrations of hydrogen peroxide, malondialdehyde, proline, soluble carbohydrate, neutral detergent fiber and acid detergent fiber in all genotypes and also changed the activities of antioxidant enzymes catalase, ascorbate peroxidase and superoxide dismutase depending on the tested genotype and salinity level. Payam and Sepideh cultivars were identified as the most sensitive and Pegah and GS4 as the most salt tolerant in both germination and field studies. In order to investigate the effects of the foliar application of growth regulators on sorghum plants two separate pot experiments were conducted each one as factorial arranged in a completely randomized design with four replications. In the first pot experiment the plants of Speed Feed cultivar were foliar sprayed with different concentrations of growth regulators (salicylic acid and ascorbic acid 0, 100, 150 and 200 mg/l, humic acid 0, 250, 500, 1000, and 200 mg/l and proline 0, 15, 30, 45 and 60 mg/l) under two salinity levels (0 and 100 mM NaCl). The results of this experiment showed that foliar application of all growth regulators through induction of an adaptive response increased potassium concentration, photosynthetic rate, stomatal conductance, chlorophyll a, b, carotenoids and proline concentrations and also the activities of antioxidant enzymes catalase, ascorbate peroxidase and superoxide dismutase but reduced sodium concentration. The optimum concentrations to achieve the most plant growth under saline condition were 30, 100, 150 and 2000 mg/l for proline, ascorbic acid, salicylic acid and humic acid, respectively. The second pot experiment evaluated the effects of five foliar application treatments (150 mg/l salicylic acid, 100 mg/l ascorbic acid, 2000 mg/l humic acid and 30 mg/l proline, based on the optimum concentration of each compound determined in the first pot experiment) on two salt sensitive (Payam and Sepideh) and two salt tolerant (Pegah and GS4) sorghum genotypes under two salinity levels (0 and 100 mM NaCl). Based on the results of this experiment foliar application of salicylic acid, ascorbic acid, humic acid and proline increased photosynthetic rate, stomatal conductance, potassium, chlorophyll a, b and carotenoids concentrations, the activities of antioxidant enzymes and shoot and root dry weights but decreased sodium, hydrogen peroxide and malondialdehyde concentrations. However, the response of sensitive sorghum genotypes to foliar application of these growth regulators were more pronounced as compared to the tolerant genotypes. The third pot experiment was conducted in a growth chamber to investigate the differences of two sensitive and tolerant sorghum cultivars in terms of the physiological and biochemical responses to inoculation with P. stutzeri . The treatments were arranged as factorial in a completely randomized design with four replications. In this experiment four salt levels (0, 100, 150 and 200 mM NaCl) were considered as the first factor, two sorghum cultivars (Payam and Pegah) as the second factor and two inoculation treatments (inoculation with distilled water and inoculation with P. stutzeri bacterial suspension) as the third factor. Keywords: Sorghum, salinity, salicylic acid, ascorbic acid, humic acid, proline, P. stutzeri .