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Self and binary mass diffusion in smectic, nematic and cholesteric liquid crystals was studied experimentally. The diffusing molecules were tagged with C-14 radioactive isotopes and the time course of their distribution in a modified Loschmidt cell was determined by liquid scintillation counting. Diffusion coefficients were obtained as functions of temperature and the strength of an applied magnetic field, which increased (when parallel to mass flux) or decreased (when perpendicular) the diffusion rate in nematic p-azoxyanisole. Application of a static electric field resulted in chaotic convection. The experimental results indicate that a mass of about 5 × 10-12 g (a swarm) is the unit of cooperative orientation in nematic p-azoxyanisole and that the microscopic fluctuations in the concentration gradient are independent of the fluctuations in the orientation of swarms.