The fractionation of active chicken tumor extracts has been continued.

1. By a rapid method of dialysis the diffusible fraction of the treated extract, representing about 75 per cent of the solids, has been eliminated without reducing the tumor-producing activity.

2. Combined methods of fractionation have resulted in the elimination of as much as 95 per cent of the total solids of the extract as inactive constituents. Since there was some concomitant enhancement of the activity of the agent the results were equivalent to a 25-fold concentration of it in terms of dry weight.

3. The chemical content of the undiffusible fraction has been determined in terms of total nitrogen, reducing substances, sulfur, phosphorus, and lipoids.

4. The evidence points to a protein and a phospholipoid as the principal constituents of the active residue. Further fractionation is being attempted with a view to connecting the tumor-producing activity with one of its remaining constituents.

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