Prolonged washing of thin slices of Jerusalem artichoke (Helianthus tuberosus) did not result in any apparent increase in the activity of the phosphatase enzymes, although the washing process is known to stimulate the activity of many other enzymes. However, treatment of the tissue in either 3×10(-5)M 2,4-dichlorophenoxyacetic acid or 10(-4)M indole acetic acid resulted in a 3-fold increase in the phosphatase activity. Significant stimulations of activity were detectable one hour after placing the tissue in the auxin. Treatment of the tissue in either kinetin or gibberellic acid failed to stimulate the activity of the enzyme. The enhancement of phosphatase activity caused by auxins could not be prevented by adding cycloheximide to the treatment solution an it is concluded that the stimulation occurred as the result of the activation of enzyme already present in the tissue rather than by the de novo synthesis of new enzyme protein.