The purpose of this study is to evaluate the efficacy of the oral administration of Lactobacillus reuteri in treating infantile colic as defined by the Rome III criteria. Forty breastfed infants aged from 29 days to 3 months will be enrolled and blinded randomized to receive orally L.reuteri or placebo. The rate of responders (reduction of daily crying time >50% compared to the baseline) will be assessed at day 7, day 14 and day 21 in both groups. The average daily crying time as well as the associated digestive symptoms will also be analyzed.