X-ray powder diffraction data and unit cells parameters for a monoclinic variety of the popular herbicide 2-chloro-N-(pyrazol-1-ylmethyl) acetyl-2', 6'-xylidide, commonly known as metazachlor, butisan, and butichlor, is presented [a=7.306(3) angstrom, b = 17.824(9) angstrom, c = 10.728(3) angstrom, beta=98.46(4)degrees, space group P2(1)/c, cell volume=1381.82 angstrom(3), Z=4]. The four strongest peaks (Irel > 25) at 8.87, 7.19, 4.57, and 4.45 angstrom are quite distinctive, thus X-ray powder diffraction provides a quick, simple, and definitive method of identifying this form of material from other commercially available herbicide products. (C) 2007 International Centre for Diffraction Data.