Three chemical compounds patented as urease or nitrification inhibitors were tested in productive noncalcareous clay loam soil fortified with known amounts of urea. Tested compounds were applied at the rates of 0, 10, 50 and 100 mug g-1 soil. N-serve was effective as nitrification inhibitor when applied at 50 mug g-1, without nitrite accumulation. Thiourea, patented as ureas inhibitor, at 10, 50 and 100 mug g-1, seemed to effect urease than nitrification which led to accumulation of nitrite at all levels. Nitrite persisted longer in 100 mug g-1 soil treatment. Potassium azide, a nitrification inhibitor, was relatively similar to N-serve but led to accumulation and persistence of nitrite at 50 mug g-1. The use of 100 mug g-1 level completely inhibited both steps of nitrification