A method is proposed for differentiating brominated carbons from chlorinated carbons by means of natural-abundance 13C NMR spectroscopy. The basis of the method is that the spin-lattice relaxation behaviour of brominated carbons is influenced by carbon-bromine scalar interactions, which can lead to shortened 13C spin-lattice relaxation times and reduced values of the nuclear Overhauser enhancement. C-Cl scalar interactions make a negligible contribution to the spin-lattice relaxation of chlorinated carbons. These effects are illustrated by measurement of the 13C spin-lattice relaxation times and integrated intensities of chloro-, bromo and iodobenzene and chloro-, bromo- and iodocyclohexane. The method is then tested on four polyhalogenated marine natural products. The results indicate that 13C relaxation measurements can be used to distinguish brominated carbons from chlorinated carbons in the case of halogenated quaternary carbons, sp2 hydridized methine carbons and some sp3 hydridized methine carbons, but not in the case of halogenated methylene carbons or gem-dihalo substituted methine carbons.