Growth room experiments with nine-week old purple loosestrife seedlings were conducted to determine if differential sensitivity existed between plants grown under flooded and non-flooded conditions. Seedlings were treated with triclopyr amine, triclopyr ester, glyphosate with and without surfactant at equimolar rates from 5.9 $\mu$mol/ha to 3.7 mmol/ha. At sublethal doses, flooded seedlings were more sensitive to herbicides than non-flooded seedlings, and triclopyr was more toxic than glyphosate. At the two highest doses differences between conditions and herbicides were not significant. Within a herbicide treatment no difference in absorption and translocation of either herbicide was found between flooded and non-flooded seedlings. Regardless of condition, more triclopyr than glyphosate was absorbed. Translocation patterns between herbicides were significantly different. Triclopyr translocated predominantly to stem and leaves acropetal to the treated leaf, whereas most of the glyphosate translocated to the roots and apical meristem. Triclopyr was metabolized more in flooded than in non-flooded seedlings.