Objective: To study the effect of sea buckthorn berries on the number and duration of common cold (CC) infections. As secondary objectives the effects on digestive and urinary tract infections (DTI, UTI), and serum C-reactive protein (CRP) concentrations were also investigated. Subjects: A total of 254 healthy volunteers were randomly assigned to receive sea buckthorn or placebo product during the study, which 233 of them completed. Results: There were no significant differences in the number or duration of CC or DTI between groups (CC: relative risks (sea buckthorn vs placebo) for the number and duration were 1.15 (95% CI 0.90-1.48) and 1.05 (95% CI 0.87-1.27), respectively). In the sea buckthorn group, as compared to the placebo, the serum CRP concentrations decreased significantly (difference in median change À0.059 mg/l, P ¼ 0.039). The number of UTI was too small to draw solid conclusions, but the results indicate the subject merits further investigation. Conclusion: Sea buckthorn berries did not prevent CC or DTI. However, a reductive effect on CRP, a marker of inflammation, and a risk factor for cardiovascular diseases, was detected.