Castor meal and ammonium sulphate were compared as nitrogen sources for the potato crop (Solanum tuberosum L.) in an experiment carried out in the Paraiba Valley. The results obtained indicated that castor meal gave significantly higher yields and a better grade of potatoes than ammonium sulphate. The more favorable effect of the castor meal is attributed solely to its effect as a nitrogen source and not to the small amounts of phosphorus and potash present in it.