36 ppm of N, as ammonium sulphate or urea, was added to the latosol (LE) and podzolic (Pml) soils, with 0 1.2, 2.4and 4.8 ppm of nitrapyrin. The soils were incubated during 150 days at temperatures between 25ºC 30ºC and at field capacity. The NO-3 concentration and the effect of nitrapyrin on nitrification inhibition was estimated. It was observed that the soil NO-3 concentration decreased significantly when ammonium sulphate and urea were associated with nitrapyrin. This indicated that nitrapyrin inhibited the nitrification of ammonium sulphate as well as of urea and showed initially greater percentage of inhibition of nitrification in LE than Pml soil. The time of action of nitrapyrin in the soil passed beyond 150 days.