1. There is a graded distribution of metamorphic activity from the inside of the anterior pituitary to the periphery. This is similar to the distribution of the phosphate content of the iodine precipitate obtained with extracts of different regions of the gland.
2. A new technique based upon iodine absorption and the reaction between the absorbed iodine and the leuco-base of malachite green is described.
3. The distribution of the staining intensity with this technique corresponds to the oxyphil affinity and the biological activity.
4. The oxyphil cells appear to be mainly concerned with the metamorphic activity.