The value of opal phytolith analysis is demonstrated in a comprehensive environmental study of a historical site, the Kirk Street Agents' House, Lowell, Massachusett. A method to measure phytolith degradation percentages is tested and shown to yield similar results to pollen corrosion indices; further research on this new method is suggested, however. Fluctuations in two classes of grass phytoliths indicate changing environmental conditions that support and expand upon changes noted in the pollen spectra. The results of the phytolith analysis are integrated with information derived from documentary research, artifactual analysis, stratigraphic interpretation, and other ethnobotanical methods to arrive at conclusions based on a truly multicomponent strategy. All lines of evidence point to a series of discrete occupational episode at the Kirk Street Agents' House coupled with con-comitant changes in the use of yard space.