Antioxidant enzyme activity was measured in salt tolerant callus tissue derived from the cultivar Coker 312 over an 8 hour period following treatment with either 0.1 M paraquat, 10 mM H₂O₂ or 100 M salicylic acid. Paraquat induced an up-regulation of catalase, peroxidase, ascorbate peroxidase, and glutathione reductase activities within 1 hour after treatment. The H₂O₂ and salicylic acid treatments resulted in significant increases in peroxidase and glutathione reductase within 2 hours and in catalase and ascorbate reductase within 8 hours. These data suggest that salicylic acid induces an antioxidant response through a pathway medicated by H₂O₂.