Four products of phosphonomethylation of hydroxylamine and its O-methoxyl-, O-carboxymethyl- and O-sulfonic-derivatives were tested as corrosion and scale inhibitors for C steel in water with increased salinity. The product of phosphonomethylation of hydroxylamine-O-sulfonic acid showed the highest inhibiting performance (corrosion rate 0,018 mm/year, corrosion inhibition efficiency 96%, scale inhibition efficiency 90%) at concn. 80 mg/dm(3) and 2 mg/L Zn(2+) ions.