The U.S. Bureau of Mines investigated anhydrous chlorination and caustic-acid leaching processes to recover ni, CO, mo, and w from waste hydroprocessing catalysts. In batch laboratory-scale equipment, the chlorination process extracted 61 to 99 pct of the metals. Final recovery was 65 to 99 pct. The caustic-acid leaching process extracted 81 to 98 pct of the metals. Final recovery was 36 to 99 pct. Chlorination processing included roasting, chlorination, hydrolysis of metal chlorides for recovering mo or w, water leaching of ni or CO from the spent charge, purification, and solvent extraction or precipitation of ni or CO from the purified solutions. Caustic-acid leach processing included naoh leaching, solvent extraction of mo or w from the naoh leach liquor, h2so4 leaching of the naoh leach residue, purification, and solvent extraction or precipitation of ni or CO from the purified solution. The estimated fixed capital cost for a commercial-scale plant processing 39,000 lb/d of waste ni-mo-al catalyst was $8 million for the chlorination process and $9.6 million for the caustic-acid leaching process. The estimated operating cost was about $0.20 and $0.40 Per pound of the waste catalyst, respectively, for the two processes.