The levels of compounds in exhaled mouth air do not necessarily reflect levels in the systemic circulation as bacteria can bio-transform substrates to produce compounds within the mouth. This should be of concern to researchers measuring breath volatiles with the aim of diagnosing systemic or metabolic conditions as very little is known about the origin of many compounds detected on the breath. This pilot study investigated the production of volatile compounds by bacterial communities present within the mouth. Solid-phase micro-extraction was used to extract volatiles from the headspace gas of two Gram-positive and two Gram-negative bacterial cultures known to be present within the mouth and from tongue biofilm microflora. Analyses were undertaken using gas chromatography mass spectrometry. Between 64 and 82 volatile compounds were detected from sampling the headspace gas above each of the cultures. Gram-negative anaerobes were found to produce more volatile sulfur compounds (VSCs) and amines. Solobacterium moorei, a Gram-positive species was however found to produce higher levels of acids, hydrocarbons, alcohols and aldehydes than the other species studied. Tongue-scrape biofilm systems at lower pH gave more hydrocarbons, ketones and fatty acids whilst at higher pH more alcohols, aldehydes, VSCs and amines were detected in the headspace. The results show that a number of compounds detected in mouth breath are produced by anaerobic bacteria in tongue biofilms. Thus, the contribution of volatiles from oral anaerobes cannot be ignored and more research is required to identify the major source of breath compounds as this will help determine their clinical significance as indicators of systemic disease or metabolic disorders in the body.