Glyphosate transport was studied using the 14C-labeled herbicide. Because glyphosate appears to undergo little metabolism in plants, detected 14C was assumed to indicate the presence of glyphosate. Leaf-girdling experiments demonstrated that 14C-glyphosate [N-(phosphonomethyl)glycine] transport in treated quackgrass [Agropyron repens (L.) Beauv. ♯3 AGRRE] leaves occurred in both leaf symplast and apoplast. Symplastic transport was toward the leaf tip and the leaf base. Apoplastic transport was toward the leaf tip only. Rhizome-girdling experiments showed that translocation of glyphosate from a treated shoot to another shoot on the same rhizome occurs primarily in the rhizome symplast. Girdling the base of quackgrass culms showed that acropetal transport of glyphosate from the rhizome into quackgrass shoots is in the apoplast and the symplast of the culms of quackgrass shoots. Excision of rhizome buds and rhizome apices indicated that the rhizome is a sink for glyphosate independent of rhizome buds or rhizome apices. The concentration of 14C-glyphosate in rhizome buds was less in plants with rhizome apices removed than in those with apices intact. The concentration of C-glyphosate in rhizome apices did not differ between plants with buds removed and those with buds intact. 14C-glyphosate applied to a girdled rhizome apex remained primarily in the apex. Some transport of glyphosate past the girdle occurred, indicating apoplastic transport of glyphosate in the rhizome. Apoplastic transport of 14C-glyphosate in the rhizome was greatest in water-stressed plants.