Studies of the nitrogen, deuteron and proton relaxation rates of liquid acetonitrile at various temperatures were carried out by pulsed N.M.R. techniques. Re-orientation of the methyl group about its symmetry axis is found to be approximately ten times faster than the re-orientation of the nitrile group. Analysis of the data provides an example of a large room-temperature contribution to the intramolecular relaxation component by a spin-rotation interaction. Previously sizeable spin-rotation interactions were considered to be insignificant for organic molecules at room temperature.