Decenylsuccinic acid (DSA) at 10(-3)m has been reported to increase the permeability of bean root systems to water without seriously injuring the plants. We have confirmed the increase in permeability at 10(-3)m, but have found that 10(-4)m DSA reduces the permeability. Both concentrations cause leakage of salts from the roots and cessation of root pressure exudation. The roots of intact bean plants are killed by 1 hour's immersion in 10(-3)m DSA, but the plants may survive by producing new roots. Up to 4 hours in 10(-4)m DSA causes only temporary cessation of growth. Comparisons are made between the effects of DSA and some metabolic inhibitors. It is suggested that DSA is acting as a metabolic inhibitor, and that increase in water permeability is the result of injury to the roots. Experiments with 3 other species indicated variations in response to 10(-3)m DSA. These could be largely attributed to differences in susceptibility to injury.