Various studies in animals and humans have shown a potential beneficial effect of probiotics consumption on allergy. However, few studies exist that document their efficacy for upper airways allergies such as allergic rhinitis. The objective of this study is to investigate the effect of short-term oral administration of a Lactobacillus paracasei on a nasal provocation test (NPT) with grass pollen, performed out of pollen season. Adult volunteers with allergic rhinitis are enrolled in a randomized, double-blind, placebo-controlled study, based on two 4-weeks cross-over periods of product consumption (probiotic-fermented milk versus placebo), separated by a washout period of 6-8 weeks. Objective and subjective clinical parameters of NPT as well as systemic and nasal immunological parameters are compared between the two treatment periods.