Of seven fluorescent dyes tested, rhodamine WT (RWT) and pontacyl brilliant pink (PBP) were the only two found to be suitable for tracer studies of water movement in plants. The results indicate that RWT is superior to PBP. The dyes were introduced in the aqueous form into the root zone of plants and were rapidly absorbed and transported to the leaves. The dosages were 1, 2, and 5 grams of dye per 32 kg of soil. With the largest dosage, the dye could be observed visually in the leaves. The concentrations of dye per gram of plant tissue ranged from 5 μg of PBP in oleander plants to 323 μg of RWT in fir plants. The time that elapsed from introduction of the dye into the soil until its detection in the leaves varied from 4 to 24 hours. Neither RWT nor PBP had produced any observable adverse effects when the plants were inspected up to 160 days after injection. Interference by the plant material in measuring the dye concentration was not a problem.