The purposes of this study were (1) to evaluate selected grasses for nitrogen fixation attributable to microorganisms inhabiting their roots and (2) to establish nitrogen-fixing bacteria on the roots of selected metal-tolerant grasses by inoculation trials. Nitrogenase activity (c2h2 reduction) was found to be associated with agropyron dasystachyum, agropyron smithii, aristida purpurea, oryzopsis hymenoides, and stipa comata. Uptake of fixed nitrogen was also demonstrated for these grasses. Two unidentified nitrogen-fixing bacteria were isolated, one from stipa comata and the other from aristida purpurea. Cynodon dactylon and agropyron cristatum were successfully inoculated with the unknown isolate obtained from stipa comata. The inoculated plants exhibited nitrogenase activity whereas uninoculated controls gave negative results.