The rate of phosphate influx, and the activity of extracellular phosphatase, were measured simultaneously in root systems of intact, sterile barley plants (Hordeum vulgare L.) of widely differing P status. Similar measurements were made on suspension cultures of rose cells (Rosa sp.) starved of P for various periods. Under the experimental conditions used, extracellular phosphatase activity greatly exceeded phosphate influx but there was a very significant correlation between the two. The possiblity of the extracellular phosphatase being involved in phosphate transport is discussed.