Irritable bowel syndrome (IBS) is a condition where abdominal pain, diarrhoea, constipation, gas distension and/or variability in the bowel habit are experienced. It has been suggested that the gut microflora may be involved in this condition and that an 'abnormal' colonic fermentation may provoke the symptoms ofIBS. In this study, the faecal flora of 11. IBS patients was compared with that of 11 healthy individuals quantitatively using fluorescence in situ hylJridisation (FISH) and· traditional plating techniques, as well as qualitatively using denaturating gradient gel electrophoresis (DGGE). It was found that IBS patients had lower total . . ./ bacterial counts, bifidobacteria, lactobacilli, bacteroides and clostridia than seen in healthy individuals. DGGE also showed differences between illS and healthy samples, especially in relation to stability ofthe microflora over time. A synbiotic version ofLactobacillus plantarum NCIMB 41114 with seven different prebiotics was tested in batch culture fermenters using faecal samples from IBS donors. From all the combinations GOS-synbiotic was chosen sirc~ it enhanced the . . growth of the probiotic and was found to be more effective in 'normalising' the . .~ faecal flora in IBS. This synbiotic combination was used in gut model· systems using faecal samples from donors belonging to different IDS subgroups. The results showed that administration of the synbiotic impacted the specific IBS subgroups .. differently, but modulated the rnicroflora towards selective stimulation of bifidobacteria and lactobacilli. In the last part of the study the amount of gas produced from IBS faecal flora during fermentation was compared to that ofhealthy faecal flora. The IDS flora produced more cumulative gas and had greater rates of production than the healthy flora. Administration of the synbiotic reduced gas production in all systems (IBS and healthy). Taken together, these observations help to define dietary management strategies, based on the gut flora and its activities, aimed towards improving IBS symptomology.