BACKGROUND: Irritable bowel syndrome (IBS) is a widespread functional disorder of the digestive tract. Its aetiology is unknown and therapeutic options are limited. Recent reports suggest that probiotics may have a role in regulating the motility of the digestive tract. AIM: To assess the efficacy of Lactobacillus plantarum 299V (LP299V) in patients with IBS. PATIENTS AND METHODS: Forty patients were randomized to receive either LP299V in liquid suspension (20 patients) or placebo (20 patients) over a period of 4 weeks. Clinical examination was performed at baseline and at the end of the study. Additionally, patients assessed their symptoms by applying a scoring system. RESULTS: All patients treated with LP299V reported resolution of their abdominal pain as compared to 11 patients from a placebo group (P = 0.0012). There was also a trend towards normalization of stools frequency in constipated patients in six out of 10 patients treated with LP299V compared with two out of 11 treated with placebo (P = 0.17). With regards to all IBS symptoms an improvement was noted in 95% of patients in the LP299V group vs 15% of patients in the placebo group (P < 0.0001). CONCLUSIONS: LP299V seems to have a beneficial effect in patients with IBS. Further studies on larger cohorts of patients and with longer duration of therapy are required in order to establish the place of L. plantarum in the treatment of IBS.