Proton spin-lattice relaxation studies were carried out in the SAand S*Cphases of the liquid crystal CI IPNOC using both conventional and fast field cycling NMR techniques.T1dispersion curves were obtained at two different temperatures for each mesophase covering frequencies from 102to 3 × 108Hz. In both mesophases theT1data can be described assuming the presence of three different relaxation mechanisms, namely local molecular rotations, molecular self-diffusion and collective motions. The self-diffusion constantD1was evaluated for several temperatures and the activation energy associated with the diffusion process was obtained. The expected contribution of the soft-mode for the spin-lattice relaxation could not be separated from the contribution of other collective motions. The correlation times associated with the rotations around the molecular long axis and with the fluctuations of this axis were evaluated for both the SAand the S*Cphases.