The bacterium, Bifidobacterium lactis HN019, has been studied for a variety of traits important to its ability to function as a probiotic. Publications documenting identity, safety, antipathogenic effects, immune enhancement, and intestinal colonization are reviewed. Most studies documenting immune effects are short term in duration (< or =6 wk feeding periods), so longer term trials would be useful to determine to what extent effects are sustained. One year-long trial feeding both galacto-oligosaccharides and HN019 in children 1 to 3 years of age provided evidence for improved growth and reduction in infection incidence. HN019 is a well-characterized probiotic strain with documented probiotic effects of meaningful magnitude especially in the area of immune system modulation.