The dissolution of pure Cu, 90/10 and 70/30 Cu-Ni alloys and of Monel 400 in strongly aerated 0.1 m HCl is studied by the weight loss technique at 25 degrees C and 60 degrees C. All four materials behave in a similar manner. The weight-loss/time curves are formed by an initial, low rate, induction period representing the dissolution of Cu in the monovalent state, CuCl2-. The nickel of the alloys dissolves simultaneously, but in quantities higher than present in the solid metal. Air oxidizes Cu+ to Cu2+. When enough of Cu2+ accumulates in solution, the dissolution of Cu is auto-catalyzed through the reaction Cu+Cu2+ = 2Cu(+). This conclusion is supported by the results of experiments in which extra Cu2+ ions are added to the solution. The rate of dissolution along the induction period increases and the period itself decreases and disappears as more Cu2+ ions are added to the acid. A rise in temperature accelerates the dissolution reaction both along the induction as well as the catalyzed stages. The activation energies of dissolution are material dependent and vary between 3 and 11 K cal/mole. The corrosion rate (CR) of the four materials along the induction period varies with the [Cu2+] of the solution according to CR = A [Cu2+](n) where A and n are constants. The value of n depends on the Cu content of the alloy. The corrosion rates along the catalyzed reaction are independent of the [Cu2+].