A large amount of research work has been done in the field of plant nutrition since 1804, when de Saussure established that the plant depends upon the soil for the supply of nitrogen and the mineral components of the ash. A better knowledge about the nutrient elements was gained after Liebig' s work, published in 1840, which demonstrated that the soil furnishes the growing plant with the elements calcium, potassium, sulfur, and phosphorus. But the great advances in the field of mineral nutrition came after the introduction by Sachs and Knop, in 1860, of the methods of liquid culture which have been ever since the basis of this type of experimentation. A marked tendency toward the study of the rate of absorption of nutrient elements by different plants began late in the nineteenth century. The idea has always been to gather sound information that can be applied practically in the attempt to make crop production a more successful enterprise, both from the economic and scientific points of view. Several factors have induced the undertaking of the present investigation: the need for more detailed Information concerning the relative absorption of some of the nutrient elements by the tomato plant at different stages of development; a complete recognition of the various factors that affect the nutrient absorption by different species of plants; and finally, the fact that most of the studies performed up to date have not considered the mineral absorption in terms of the amounts taken up by the plant per unit produced of fresh and dry weights respectively. It is, therefore, the purpose of this work to present data concerned primarily with the relative absorption of some nutrient elements by the tomato plant at five stages of growth. Emphasis is placed on the cations calcium, potassium, and magnesium. Other elements also included in this study were phosphorus and nitrogen.