Previous studies have revealed increased levels of antioxidants such as peroxidase, catalase, ascorbate peroxidase, superoxide dismutase, and glutathione reductase in NaCl stressed cotton callus (Gossypium hirsutum L.) and plant. Another study has revealed an elevation of the antioxidant glutathione S-transferase (GST) during salt stress in cotton callus and plant. This study was designed to determine the isozyme pattern of GST in callus grown at 0 mM NaCl and 150 mM NaCl using 1-chloro-2,4-dinitrobenzene (CDNB) and ethacrynic acid (ECA) as substrates. GST revealed four major and two minor isozymes in the salt stressed callus versus one isozyme in the control callus using CDNB as substrate. Six major isozymes were evident in both the control and salt stressed callus when ECA was provided as substrate. Substrate specificity and both isozyme enhancement and induction are evident when the cotton callus is subjected to NaCl stress. GST's induction when salt stress is applied may impart an increased ability for the plant cell to respond to NaCl associated lipid peroxidation.