Interatomic distances of isotopically doubly labeled N-Acetyl-Pro-Gly-Phe crystals, obtained from rotational echo double resonance (REDOR) experiments, were analyzed as a three-spin system in which observed nuclei are simultaneously coupled with isotopically labeled intra- and intermolecular heteronuclei. In particular, the intermolecular dipolar interaction was examined to obtain a clue as to the relative orientation of a given molecule to the surrounding neighbors. We have developed a systematic procedure to determine both the intra- and intermolecular interatomic distances and the angle between these two interatomic vectors. The former intramolecular distances were determined by fitting the infinitely diluted normalized REDOR differences Delta S/S-0 values to the theoretical curve as a two-spin system. Then, Delta S/S-0 values from undiluted doubly labeled samples were analyzed as three-spin systems. Subsequently, the interatomic distances and the angles, between the two isotopically labeled nuclei belonging to the same and different molecules, were determined by a systematic search for the most probable area based on analysis of the two series of Delta S/S-0 values by two- and three-spin systems. The precision and accuracy of the intermolecular parameters thus obtained were evaluated by comparing the data with those of X-ray diffraction with and without correction of thermal vibration. The effect of additional nuclei on this procedure was also examined as four-spin system.