[en] The structure determination of biological macromolecules by single-crystal diffraction techniques requires an experimental solution of the phase problem inherent in the structure analysis. This chapter describes a method for the phase determination which uses the nuclear resonance scattering of an ⁵⁷Fe nucleus as reference. The basic features of the method are discussed and different techniques are compared. The pertinent amplitude for nuclear resonance scattering is derived. First test experiments on single crystals of myoglobin are described. Technical problems arise from the necessity of using gamma-ray sources with limited intensities. In particular, the optimization of ⁵⁷Co sources, the development of large-area position-sensitive proportional counters, and the necessary freezing of protein crystals are discussed. The measuring time required for a structure determination of bacterial catalyse is estimated. (orig.)