In view of the rather surprising distortions reported in the dimensions of the para-dinitrobenzene molecule1, a redetermination of this structure was recently attempted in this laboratory. The results of our preliminary two-dimensional survey did not point to a completely symmetrical molecule, but indicated that either (a) the planes of the nitro-groups may be slightly inclined (about 5°) to the plane of the benzene ring, or (b) the nitrogen – oxygen distances within the nitro-groups may not be equal, but differ by about 0·05 A. We were unable to distinguish between these alternatives by two-dimensional X-ray methods. In the meantime, we have learned that a full three-dimensional analysis of this structure has been undertaken elsewhere, so we have not pursued the matter further. The final results will be awaited with interest.