The temperature dependence of the spin-lattice relaxation times of protons in air-free acetyl chloride (CH 3COCl) methylene bromide (CH 2Br 2), ethylene bromide (CH 2BrCH 2Br), methyl acetate (CH 3CO 2CH 3) and nitromethane (CH 3NO 2) were investigated. The experimental results show that the dominant relaxation mechanism is the proton-proton dipolar interaction and the theoretically calculated values are in good agreement with the obsered ones. This shows that the Stokes frictional coefficients for the diffusion of molecules in pure liquids should be modified by microviscosity factors f r= 1 6 for rotational and f t= 1 2 for translational motions.