The preparation and gas chromatographic mass spectrometric properties of a number of vinyldimethylsilyl ethers of steroids and cannabinoids are reported. Gas-liquid chromatographic retention increments for the vinyldimethylsilyl ethers were about 1 methylene unit higher than those of the corresponding trimethylsilyl ethers for each derivatized hydroxyl group. The mass spectra were very similar to those of the correspondig trimethylsilyl derivatives with, in many cases, enhancement of the abundance of both the molecular ions and diagnostic fragment ions containing silicon. These properties made vinyldimethylsilyl derivatives useful for: (a) mass spectral interpretation by the shift technique; (b) correlating spectra with those of the trimethylsilyl derivativeds when vinyldimethylsilyl derivatives were used to shift diols from monohydroxy compounds in gas chromatograms; and (c) for determining the major site of RMe2SiOH loss in the mass spectra of mixed trimethylsilyl/vinyldimethylsilyl derivatives.