Background Animal and human studies have suggested that yogurt containing live active bacteria leads to improved immune and clinical responses. Specific benefits of yogurt containing L. acidophilus on allergic asthma have been hypothesized but not studied. Methods In a crossover double-blinded design, the effect of live active yogurt (225 g twice daily) with or without L.acidophilus was studied in 15 adult patients with moderate asthma. Immune and clinical parameters were measured before and after the two 1-month crossover phases. Results No significant changes were noted in peripheral cell counts, IgE, IL-2, or IL-4 when comparing the two diets to each other. Concanavalin A-stimulated lymphocytes from patients who consumed yogurt containing L. acidophilus produced borderline elevated interferon gamma levels (P =.054). No differences were noted in mean daily peak flows or changes in spirometric values. Quality of life indices were unchanged when comparing the two groups. Conclusions Yogurt containing L. acidophilus generated trends in the increase in interferon gamma and decreased eosinophilia; however, we were unable to detect changes in clinical parameters in asthma patients in association with these modest immune changes.