Vibrational band intensities of CH and CH$_2$. groups in haloforms and methylene halides have been measured in the vapour phase, and for solutions in carbon tetrachloride. Marked variations of band intensity in the vapour phase occur along the series fluoroform, chloroform, bromoform, and the relative intensities of the first overtone bands also show interesting differences. With solutions in carbon tretrachloride the band intensities are often increased considerably. Similar data have been obtained for the symmetric and antisymmetric CH$_2$ group vibrations of the methylene halides. An interpretation of some of the results has been suggested in terms of the polar properties and electrical anharmonicity of the vibrating bonds. The effect of solvent observed again emphasizes the importance of solute-solvent interactions, even in non-polar media.