A rapid method for determining residues of the herbicide imazapyr in water and soil is described. The soil samples were extracted with aqueous methanol and, after concentrating, the residue was estimated by HPLC with UV detection at 250 nm. Imazapyr dissolved in water was quantified by injecting the samples without any previous treatments. Analyses were performed without clean-up of soil and water samples. The pre-concentration of samples was required only at very low herbicide amounts. The maximum recovery was achieved by methanol/water (3:2 v/v) with both soils after three extraction procedures. The detection limits were 0.01 mg/l and 0.05 mg/kg in water and soil, respectively.