A rapid, highly sensitive, and selective method was developed for the identification and quantitation of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) in wheat plants, wheat grain, and soil by ultra-performance LC/MS/MS. MCPA was extracted from the sample (5 or 10 g) with acetonitrile, and an aliquot was taken for cleanup with primary secondary amine. Two precursor product ion transitions for MCPA were measured and evaluated to provide maximum confidence in the results. Average recoveries from wheat plants, wheat grain, and soil fortified at levels of 0.01-1.0 mg/kg ranged from 75.1 to 93.9%, with RSD(r) values of 3.0-9.3% and RSDR values of 3.1-8.7%. Coefficients of determination of R2 > or = 0.9994 were obtained for wheat and soil matrix calibration curves at MCPA levels of 0.01-5.0 microg/mL. Under conditions of electrospray ionization in the negative-ion mode, the ion at m/z 141 was monitored for quantitation; the parent ion at m/z 199 was also measured. The LOD values for MCPA in wheat plants, wheat grain, and soil were determined to be 0.005, 0.004, and 0.004 mg/kg, respectively, and corresponding LOQ values were 0.02, 0.01, and 0.01 mg/kg. This method can be used to determinate MCPA residues in wheat products and soils.