In the present study, the immune-modulating efficacy of a polyphenol-rich beverage on symptoms associated with the common cold was evaluated. For this purpose, ninety-eight patients reporting common cold symptoms that began no longer than 24 h before the study intervention were randomly assigned to consume either the test beverage or placebo twice per d for 10 d. The severity of the disease was expressed as the total score of the five cold symptoms ‘general feeling of sickness’, ‘headache and/or joint aches’, ‘sore throat and/or difficulty swallowing’, ‘hoarseness and/or cough’ and ‘stuffy nose/sniffle’. Consequently, the decrease from 10·2 (sd 3·1) points at the beginning to 2·1 (sd 2·7) points by the end of the study in the verum group demonstrated a clear improvement, whereas in the placebo group only a reduction from 10·5 (sd 3·0) to 6·3 (sd 3·8) points could be observed. The mean difference between the groups (primary efficacy criterion) of 3·9 points was highly significant (P < 0·01). At the end of the study there were highly significantly (P < 0·01) more patients in the verum group complaint free than in the placebo group (secondary efficacy criterion). In addition to these self-reported values, several local findings of the physical examination were also significantly improved in the verum group.