The revegetation of sterile acid mine spoils is a costly and lengthy process due to the many factors (pH, toxic materials, low nutrients, poor soil structure, temperature, moisture, length of growing season, etc.) which impede the establishment of stable plant communities . A microbial bioassay t echnique applied to soil systems has been developed to allow a rapid (four weeks) and integrated (with respect to nutrients and toxicants) determination of the best amendments for stabilizing mine spoils by revegetation. Using mine spoil from the Blackbird Mine, Cobalt (near Salmon), Idaho, various comb illations of nitrogen, phosphorus, chelaors, trace elements, potassium, manure and sal t leaching were studied with the bioassay by observing microscopically and by measuring nitrogen fixation and accumulation, dehydrogenase activity, chlorophyll~ accumulation, and other chemical parameters. It was concluded that the limiting factors for microbial (algal) growth were, in order of importance, pH control, soil moisture, and phosphorus. Other treatments failed to show statistically significant better results over the control. The fate of phosphorus in the spoil and its effecton growth response kinetics is also speculatively discussed.