Kováts retention indices can be used to characterize the gas chromatographic behavior of C1and C2halocarbons on Porapak Q. Within each series of halocarbons the retention index increases with chlorine content, decreases with fluorine and hydrogen content, and is directly proportional to molecular weight and boiling point. Substitution of a fluorine or a bromine atom for a chlorine atom in these compounds results in characteristic changes in the retention index. The heats of adsorption are in the neighborhood of the latent heats of vaporization for the compounds examined.