Field trials were carried out using an aerial spray of Magniosan 55 (55 per cent magnesium nitrate) for the correction of severe magnesium deficiency in a Valencia orange orchard. Two treatments were applied, in autumn and spring respectively, each containing 50 l. Magniosan 55 solution in 200 l. water per hectare. The spray did not cause damage to fruit or leaves, penetrated satisfactorily into the lower and interior part of the canopy, and increased the Mg content of the leaves of treated trees from 0·095 to 0·190 per cent.