Experimental techniques are described for conducting greenhouse tests to examine the pathways for phytoremediation of volatile organic compounds (VOCs), distinguishing between uptake of the VOC along with water transpired by living plants and the passive, physical process of volatilization. The experimental techniques were applied to assess the potential for phytoremediation of methyl-tertiary-butyl-ether (MTBE). Experimental data indicate that MTBE was readily taken up from water by hybrid poplar saplings, yielding 25% reduction in aqueous MTBE concentration and 30% reduction in MTBE mass over a 1-week period. These reductions in plant systems were significantly greater than in controls, indicating great potential for MTBE phytoremediation in the field. Engineering parameters for phytoremediation were determined from the experiments, yielding an MTBE transpiration stream concentration factor of 1 and a root concentration factor of 0.7–1.4. Mass balance studies showed good closure on MTBE mass balance, indicating no significant degradation of MTBE in the young poplar saplings used in this study. These results suggest that phytovolatilization may be the primary pathway for MTBE phytoremediation.