Researchers from the U.S. Bureau of Mines have been conducting a series of laboratory studies to examine the general characteristics of metal dissolution from mine wastes, as well as possible chemical control strategies. The studies reported upon in this paper involved samples of sulfidic waste rock obtained from a gold-mining operation. Experimental methods included columns, perforated baskets, and Buchner funnels, coupled with humidity and controlled-atmosphere chambers. Results indicated that concentrations of soluble metals were one to two orders of magnitude higher in the leachate obtained during the initial two or three leachings than in leachates collected later. During the initial seven teachings, samples stored and leached under nitrogen produced the same metal leachate concentrations as samples stored and leached in laboratory air. The biocide sodium benzo-ate had little effect on the initial phase of dissolution, although another biocide, sodium lauryl sulfate, did reduce initial metal mobility. This effect appears to be related to the surfactant properties of the sodium lauryl sulfate on the stored contaminants and not to a decrease in biological activity. During the second phase of leachings, the use of biocides and/or the exclusion of oxygen reduced metal dissolution and sulfate production. Results indicated that two reaction pathways, biologic and oxidation by air, contributed nearly equally to metal dissolution and sulfate formation.