A monocysteinic mutant of poplar glutaredoxin (C30S) has been overproduced and purified. The protein has been crystallized in complex with glutathione using the hanging-drop vapour-diffusion technique in the presence of PEG 4000 as a precipitating agent. A native data set was collected at 1.55 A resolution. The crystals belong to space group P2(1)2(1)2(1), with unit-cell parameters a = 45.7, b = 49.1, c = 104.8 A. Isomorphous crystals of a selenomethionine derivative were grown under the same conditions. Three data sets were collected at 1.73 A using the FIP synchrotron beamline at the ESRF. The positions of the Se atoms were determined and model rebuilding and refinement are in progress.