Effects of flooding the root system on nitrogen status, leaf chlorosis and shoot growth have been studied in barley seedlings. Within 2 days, oxygen in the soil water decreased to a low concentration (< 2%), and net uptake of nitrogen to shoots was inhibited. Simultaneously, there was a decrease in the average concentration of nitrogen in shoots, due to translocation from older leaves to younger expanding ones. These changes pieceded the onset of chlorosis of the older leaves. It is suggested that inhibition of nitrogen uptake, and the consequent redistribution of nitrogen within the shoot, are important contributory factors in the early senescence of leaves and the retarded growth of shoots in flooded plants.