The Bureau of Mines investigated a silver-catalyzed oxidative procedure for leaching an arsenical copper sulfide concentrate containing 10 pct as and 32 pct cu. Currently, there are no environmentally safe means to treat arsenical copper concentrates in the United States. Leaching was conducted in a 2-l autoclave reactor. The effects of catalyst concentration, o2 pressure, temperature, and h2so4, cu, as, and fe concentrations in the leaching solution on extractions of metals from the concentrate were determined. The best leaching conditions for extracting 95 pct cu and as and less than 21 pct fe were 260 g/l concentrate, 0.007 Mol/l (1.0G/l) agcl, 3.0 Mol/l (294 g/l) h2so4, 100 deg c, 60 psig o2, and 6 h. Copper as cuso4.5H2o was recovered by crystallization from the pregnant solution. Arsenic, as as2o3, was recovered from the copper mother liquor by solvent extraction, with tributyl phosphate, so2 reduction of as5+ to as3+ in the strip solution, and crystallization of the as3+. The silver catalyst was recovered by contacting the leached residue with a brine solution. A conceptual scheme is proposed for treating arsenical copper sulfide concentrates.