Two laboratory experiments were conducted to study the effects of salt and nitrogen-sulfur compounds on the transformations of nitrogen in three Arizona soils. In the first experiment the effect of NaCl in concentrations of 0 to 1 m (molal) at moisture levels of 1/3 and 15 bars was studied in the Gila and Laveen loam soils. At 1/3 moisture nitrification of urea-¹⁵N and native soil nitrogen was appreciably reduced only at 1 m salt level. At 15 bars moisture, nitrification was almost completely inhibited by the 1 m salt concentration. Mineralization of soil nitrogen was reduced more by decreasing moisture than by increasing salt concentrations. Ammonia volatilization was increased by both salt and moisture stress and was associated with inhibition of nitrification. Slight effects of salt were observed on ¹⁵N immobilization and ¹⁵N recovery (including volatilization). In the second experiment nitrogen-sulphur combinations (¹⁵N labelled) of KNO₃, KNO₃ + S, urea, urea + S, APS (ammonia polysulfide) and Thiosul (ammonium thiosulfate) were studied at field capacity (FC) and 1.5 FC moistures. In the calcareous Gila soil nitrification was suppressed by the presence of sulfur at 1.5 FC moisture. Volatilization losses were appreciable only from APS. Immobilization of ¹⁵N was greatest from treatments with the higher sulfur rate (elemental S). Denitrification was slightly increased by sulfur at FC, however, at 1.5 FC dramatic losses occurred by denitrification (autotrophic in the presence of sulfur, especially with elemental S. The nitrifying ability of the slightly acid and coarse textured Sonoita soil was low. Nitrification was suppressed more by the presence of sulfur at both moistures. Ammonia volatilization was appreciable from APS followed by urea. ¹⁵N immobilization was high from urea followed by APS. Appreciable losses by denitrification occurred only with APS. The Sonoita soil showed a lower sulfur oxidizing power than the Gila with the only appreciable rate of oxidation from Thiosul followed by APS.