Pyrazon (5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone) was absorbed by the roots of both common lambsquarters (Chenopodium album L.) and sugar beets (Beta vulgaris L.) and translocated in an acropetal direction to all parts of the plant. Common lambsquarters plants accumulated greater amounts of 3H-pyrazon per gram of tissue than did sugar beet plants and this was especially true of leaf tissues. Translocation into the leaves of both species occurred equally into mature and developing leaves. Neither basipetal nor acropetal translocation of pyrazon occurred following leaf applications of 3H-pyrazon. Pyrazon accumulated in the leaves of common lambsquarters, but it was metabolized when absorbed into sugar beets. Roots, petioles, and leaf blades of beets rapidly metabolized pyrazon while only roots metabolized pyrazon in common lambsquarters. Selectivity of pyrazon appeared to be associated with the rate of metabolic breakdown occurring in the leaf. Accumulations occurred in the susceptible common lambsquarters plant while metabolism kept pace with uptake in the leaves of the tolerant sugar beet plant.