We present the first results from a dedicated survey with ISAAC on the Very Large Telescope (VLT) to constrain variations in the fine‐structure constant &agr; in the range 2 <z< 3 using the forbidden [O III] transitions at 4959Å and 5007Å, as pioneered at lower redshift by Bahcall et al. (2004). We describe our data analysis in detail and show that we can use the atmospheric OH lines to wavelength calibrate the spectra to very high accuracy. The resulting method gives useful constraints but further work remains to remove sources of systematic uncertainty. © 2004 American Institute of Physics