The partially depolymerized hyaluronic acid (PDHA) was prepared as follows: Na hyaluronate from a virulent strain of group A Streptococcus pyogenes was incubated at 38[degree] C for 15 min. with testicular hyaluronidase, autoclaved for 40 min., and then centrifuged. The clear supernatant soln. assayed less than 0.1 TRU hyaluronidase/ml. In rabbits highly polymerized hyaluronic acid from S. pyogenes, bovine vitreous humor, and human umbilical cord had no significant effect as spreading agents; however, PDHA was quite effective and 12 mg. produced areas of spread approximating that obtained with 2000 TRU hyaluronidase. In hypodermoclysis 150 mg. PDHA was as effective as 150 TRU hyaluronidase; in both cases the rate of the clysis was 2.5 times faster than in the saline controls. Similarly, these doses injd. into groups of guinea pigs along with a radio-opaque substance produced comparable spreading; the areas were about double those of the controls and the time required for the contrast media to appear in the urinary bladder was about half that of the controls.