The metabolic fate of pencycuron [1-(4-chlorobenzyl)-1-cyclopentyl-3-phenylurea] in rice plants was investigated with [phenyl-U-^<14>C] compound. When the leaves were treated with ^<14>C-pencycuron radiocarbon gradually penetrated into the leaf tissues and part of them showed an acropetal movement. Most radiocarbon was, however, retained on the leaf surface. Pencycuron always remained as a major component (52% of the applied dose after 40 days) and its metabolites were relatively minor in amount (7% of the applied dose). The metabolites identified were : 1-cyclopentyl-3-phenylurea (IV), 1-(4-chlorobenzyl)-3-phenylurea (V), 1-(4-chlorobenzyl)-1-(cis-3-hydroxycyclopentyl)-3-phenylurea (XI) and its trans isomer (XII), and glucosides of (XI) and (XII). Unextractable radiocarbon increased with time from 0.9% (1 day) to 16.5% (40 days). When ^<14>C-pencycuron was sprayed twice on rice plants before heading and at the heading stage, radioactive residues in rice grains were found 0.56 ppm as a pencycuron equivalent, but the radiocarbon was mainly localized in the bran (85%). Intact pencycuron was detected 0.018 ppm in hulled rice and 0.003 ppm in polished rice. Radiocarbon in grains mainly remained as an unextractable bound residue
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