IN connexion with experiments on enzymatic decomposition of wheat straw xylan1, the xylanase activity in the soil has been investigated by a method very similar to that of Hofmann2. To 5 gm. of air-dry soil in 50-ml. Erlenmeyer flasks were added 2 ml. of toluene, and, after 10 min., 5 ml. phosphate buffer (pH 6.5) and 5 ml. xylan solution, or 5 ml. water in the blanks. The stoppered flasks were placed in an incubator at 37° C. and shaken now and then. Samples were taken out by means of a pipette and centrifuged, and reducing power was determined in 1 ml. of the supernatant by the Somogyi method3. Soil samples were taken from unfertilized, artificially fertilized and farmyard manured plots in fertilizer experiments at Danish Government field experiment stations.