The information presented in this paper clearly demonstrates once more the outstandingly beneficial effect of magnesium on yields of pineapples when gro'wn on the acid latosols, soils typical of t~ pineapple growing region of Puerto Rico. Pineapple plants supplied with magnesium produced the average 2.75 tons more fruits per acrA. than plants not supplied with this nutrient. This was equivalent to a 20 percent increase in yields. Foliar analyses revealed that highest fruit yields were associated with the highest leaf magnesium contents. Neither the use of lime alone or in combination with magnesium were effective in increasing significantly pineapple yields. From the results presented herein it may be concluded that magnesium should be incorporated in the fertilizer mix or appl ied in foliar sprays, as may be more advantageous in a particular situation so as greatly to increase economical pineapple production.