Diatomaceous earth (DE) has been touted as a natural and effective way to control gastrointestinal (Gl) parasites in sheep. In this study, grazing lambs were fed DE at 5 and 10 percent of a supplemental ration for periods from 66 to 117 days. Weight gains, hemoglobin, packed cell volume, fecal egg/gram counts, and abomasal Gl larval counts were not different in controls vs. DE-fed lambs, although there was a trend toward lower fecal egg/gram counts in DE-treated lambs. DE by itself was not shown to be an effective parasite control agent, but could be used as part of a parasite control program.