Escherichia coli elongation factor Tu-GDP (EF-Tu-GDP) was crystallized in the presence of novel inhibitors. The only crystals which could be grown were epitaxially as well as merohedrally twinned, highly mosaic and diffracted to a resolution of 3.4 A in space group P3(1)21, with unit-cell parameters a = b = 69.55, c = 169.44 A, alpha = beta = 90, gamma = 120 degrees . To determine whether an inhibitor was present in the crystal, a poor-quality X-ray diffraction data set had to be processed. The three-dimensional structure was ultimately solved and the original question answered. The results also reveal a new type of dimer packing for EF-Tu-GDP.