Vibrational spectra of vapor-phase ethanethiol and tert-butylthiol have been recorded in the 1000 to 12 000 cm−1 region. Both the gauche and trans conformers of ethanethiol are observed. The intensities of SH-stretching vibrations are found to be significantly weaker than the equivalent CH-stretching vibrations and the OH-stretching vibrations in the corresponding alcohols. The relative strength of the SH-stretching vibrations in ethanethiol and tert-butylthiol compared with the OH-stretching vibrations in the corresponding alcohols are 0.2 in the fundamental region and 0.03 in the overtone regions. The SH- and OH-stretching intensities have been modeled with an anharmonic oscillator local mode model with ab initio calculated dipole moment functions. The weak nature of SH-stretching transitions is shown to be a result of both low anharmonicity of the vibrational mode and relatively small dipole moment derivatives.