This paper describes Bureau of Mines investigation of a silver- catalyzed oxidative procedure for leaching an arsenical copper sulfide concentrate containing 10 pct as and 32 pct cu. 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 leaching conditions for extracting 95 pct cu and as and less than 21 pct fe were 260 g/l concentrate (22 pct solids), 0.007 M(1.0 G/l) agcl, 3.0M(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 by solvent extraction of the copper mother liquor with tributyl phosphate, so2 reduction of as5+ to as3+ in the strip solution, and crystallization of the as3+. Silver catalyst was recovered by brine leaching of the leached residue. A conceptual process was proposed for treating arsenical copper sulfide concentrates.