The absorption and translocation of the isopropylamine salts of14C-glyphosate and14C-imazapyr were compared in established terrestrial alligatorweed. Results indicated that more than twice as much imazapyr as glyphosate was absorbed by treated leaves of alligatorweed. In addition, more imazapyr was translocated to the underground storage tissues in alligatorweed than was glyphosate. This difference in translocation to roots and subterranean storage tissues is proposed as a mechanism for tolerance of alligatorweed to glyphosate and susceptibility to imazapyr.