Phosphorus deficiency (P deficiency) caused a 10-20�fold increase in phos-phatase activity of S. oligorrhiza homogenates. Specific staining showed that phosphatase in control plants was located primarily in and around the vascular strands, and in P�deficient plants it was located in the epidermis of the root and undersurface of the frond. Dissection experiments showed that roots of P�deficient plants contained a disproportionately high phosphatase activity. When plant and root homogenates were fractionated, phosphatase activity was recovered in the supernatant rather than in any cell particle fraction. However, intact plants released very little phosphatase to the external medium.