The presence of nitric oxide synthase (NOS) in cotton callus Coker 312 was studied. The immunoblot analysis of cytosolic extracts with a polyclonal antibody against the C-terminus region of murine iNOS revealed an immunoreactive protein of 130kDa. The evidence presented by measuring the conversion of L-[¹⁴C]arginine to L-[¹⁴C]citrulline assay indicates the production of nitric oxide as an adaptive mechanism of plants under NaCl induced physiological stress.