Phyllochlorine ester, a derivative of chlorophyll, is a suitable example for the study of diffuse X-rays scattered by thermal waves in crystals. The investigation was concerned with whether this diffuse scattering can be used advantageously for the determination of characteristic groups in complicated molecule structures. It was found that certain atomic configurations in the molecule can be recognized clearly in the diagram of the diffused scattering. In the case of phyllochlorine ester, it is the porphyrine ring which is recognized due to the dynamical attachment of its atoms to a rigid atom group. The diffuse scattering reveals these groups easier than the crystal reflections. It is proved experimentally that the distribution of diffuse scattering has no relation to the F ourier transform of the unit cell. This method, therefore, cannot be used directly for the determination of the phases of the crystal reflections.