Abstract. The polymorphism of n-hexatriacontane (C3JI74) was investigated by X-ray diffraction and DSC thermal analysis. C3JI74 displays at least two stable monoclinic phases and a rotator phase. Starting from a solution-grown sample of very high purity the following phases are observed with increasing temperature : MOI 1 < 345K < M101 < 346K < RIII < 348K < liquid. Depending on the thermal treatment also other forms may be observed. During these transitions, both the crystalline volume and the lamellar thickness increase. The higher order reflections of the layer structure was precisely measured by X-ray diffraction. Using a Fourier synthesis, electron density profiles of the three phases were analysed. The results show that the interlamellar structure is disturbed by increasing molecular motions with elevating températures. For some homologous alkanes also p (T) phase diagrams and binary systems have been studied.