The effect of different growth media on the types and intensities of volatile organic compounds (VOCs) emitted by Staphylococcus aureus has been investigated using a proton transfer reaction mass spectrometer (PTR-MS). The microbial culture was grown in three different broths (nutrient, dextrose and brain heart bovine). Sterile sampling flasks contained either actively growing S. aureus or uninoculated broth. The headspace VOCs in these flasks were sequentially sampled and analysed. From the mass spectra obtained we selected the product ions (resulting from emissions from the inoculated samples) to monitor changes in their intensities as a function of time. Whilst the VOCs emitted by S. aureus in each medium were observed to be the same, the time-dependent pattern of growth showed marked differences and intensities between the different growth media. We conclude that PTR-MS provides sufficient sensitivity for in vivo microbial diagnosis: this could lead to more rapid treatment of bloodstream infections, particularly crucial for the well-being of immunocompromised and intensive care patients.