In this paper results obtained with the phenomenon of ammonification and nitrification in several nitrogen fertilizers are presented. The objective was the determination of the intensity and evolution of these phenomena. For this purpose an experiment was set up including the following nitrogenous fertilizers: ammonium sulfate, urea, castor bean cake, blood meal, horn and hoof meal and calciumcyanamide. The experiment was conducted during 40 days; after each ten days period, samples of the different treatments were taken and ammoniacal and nitric nitrogen were determined. The results obtained show that the calciumcyanamide fertilizer ammonified more intensively, being followed by urea, castor bean cake, blood meal and finally horn and hoof meal. On the other hand concerning the phenomenon of nitrification, the results indicate that the castor bean cake nitrified the most, being followed in descrescent order by urea, horn and hoof meal, blood meal and ammonium sulfate. Results of calciumcyanamide analyses always presented traces of nitric nitrogen, showing that practically no nitrification ocurred during the 40 days of the experiment.