Irritable Bowel Syndrome (IBS) may be diagnosed on the presence of symptoms, according to Rome II criteria and some studies have shown that abnormal colonic fermentation may be an important factor in the development of symptoms in some patients with IBS. Since the fermentations of substrates by the intestinal flora may play a key role in the use of probiotics in the treatment of IBS, fifty patients (24 males,26 females), mean age 40 years (range = 26–64 years) with IBS, according to Rome II criteria, were enrolled into the study after informed consensus. Patients were randomly assigned to receive either the active preparation containing Lactobacillus Plantarum LP0 1 and Bifidocterium Breve BR0 both at a concentration of 5 × 10⁹ CFU/ml, or placebo powder containing starch identical to the study product, for 4 weeks. To evaluate treatment efficacy two different scores were considered: Pain score in different abdominal locations after treatment decreased in probiotics group of 38% versus 18% (P < 0.05) of placebo group after 14 days and of 52% versus 11% (P < 0.001) after 28 days. The severity score of characteristic IBD symptoms significantly decreased in probiotic group versus placebo group after 14 days 49.6% versus 9.9% (P < 0.001) and these data were confirmed after 28 days (44.4% versus 8.5%, P < 0.001). In conclusion, short-term therapy with Lactobacillus PlantarumLP0 1 and Bifidocterium Breve BR0 may be considered a promising approach to the therapy for IBS.