The preferred nitrogenous fertilizer in commercial plantations of pineapples is ammonium sulfate, according to Johnson (16). When sulfate of ammonia is used, the ammonium ion is oxidized to nitrate by soil microbiological activity, with an associated increase in soil acidity which renders iron more soluble. At the same time, both ammonium and nitrate ions are generally simultaneously available to the pineapple roots. Sodium nitrate is generally inferior and usually produces an atypical light-green color in leaves and unripe fruit of the pineapple. When sodium nitrate is used under dry conditions, however, there may be accumulation of sodium bicarbonate in the soil as reported by Kelley and Thomas (17) caused by a greater rate of uptake of nitrate than of sodium by roots and by soil microflora, a phenomenon likely to cause precipitation of iron in the soil and associated plant chlorosis. Efficient nitrogen fertilization of pineapple plants depends greatly on an understanding of the interrelationships of nitrate and ammonium ions with (a) the inorganic nutrient complex of the soil, that is, the relative concentrations of nutrient elements other than N03~ or NH4+; (b) the activities of the microflora in the soil ; and (c) shifting of pH values, and changes of temperature and moisture affecting the concentrations of these ions in the soil. It is also important to know the nitrogen requirements of plants at different growth stages on the basis of nitrogen inventories within the soil and plant tissues. This paper reports plant weights attained by one-year-old Ananas comosus grown in solution cultures with 140.0 or 2.8 mg. of nitrogen in nitrate or ammonium form and the content of ash, water, relative electrical resistance, potassium, calcium, magnesium, phosphorus and iron in the tissue.