This paper describes the determination of the nitrate, ammonium and urea nitrogen content in fertilizers. The ammonium and urea nitrogen were determined directrly in the water extract of the fertilizer. The nitrate nitrogen was separated by a column of resin DOWEX-1-X8, strongly basic. Nitrate was determined after the elution with 20% NaCl solution. The procedure described requires less working time than the classical method and yelds accurate results.