The specific deuteration of olefins using tris rhodiam chloride as a Lomogeneous catalyst has been investigated. Seventeen n-monoolefins were deuterated and the distribution and the vicinal positions of the deuterium atoms were located by mass spectrometry. Deuterium adds specifically across the double bonds in n-monoolefins and the reaction proceeds to completion in a reasonable time. The mass spectral fragmentation patterns for the deuterioalkanes formed by this specific labeling technique can be used to locate the deuterium atoms and thus to determine the position of the double bond in the original olefin.