Both carrot (Daucus carota L.) and common ragweed (Ambrosia artemisiifolia L.) plants metabolized 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron). Traces of all of the following derivatives of linuron were detected in both plants: 3-(3,4-dichlorophenyl)-1-methoxyurea, 3-(3,4-dichlorophenyl)-1-methylurea, 3-(3,4-dichlorohenyl)urea, and 3,4-dichloroaniline. Differences in absorption and concentration of these derivatives were observed between carrot and ragweed plants. All of the above derivatives were phytotoxic to common ragweed plants except for 3-(3,4-dichlorophenyl)urea and 3,4-dichloroaniline, while none of the derivatives were phytotoxic to carrot. In carrot, 87% of the applied linuron was metabolized to nonphytotoxic derivatives compared to only 13% in common ragweed plants. It appears that a combination of differences in absorption, metabolism, and phytotoxicity of several of the metabolite derivatives of linuron to carrot and common ragweed plants may be the primary reason for differences in sensitivity of these two plants to linuron.