Atomic coordinates for pig insulin in the cubic crystal have been refined by reciprocal-space methods to an R factor of 0-173 for data between 10-0 and 1.7 A resolution with structure-factor amplitudes greater than two standard deviations. Stereochemical parameters for the refined model are close to standard values and the estimated error in the positions of well-ordered atoms is about 0.1 A. Residues directly involved in the formation of the exact (crystallographic) cubic insulin dimer are oriented similarly to * Current address: