Yoghurts (four varieties), prepared using Streptococcus thermophilus and Lactobacttlus delbrueckii ssp. bulgaricus and containing three probiotic strains, Bifidobacterium animalis Bb-12, L. acidophilus La-5 and L. rhamnosus GG, were examined for viability over a month of refrigerated storage. At 1, 7, 14, 21 and 28 days of refrigerated storage, the yoghurts contained stable viable populations of B. animalis Bb-12, L. acidophilus La-5 and L. rhamnosus GG, with no significant changes between intervals (P > 0.05), populations remaining at 8.0 to 8.7 logjo viable cells/mL for the projected shelf life. Decreases in pH between storage intervals appeared to reduce the viable populations of probiotic bacteria in each yoghurt (P > 0.05). Low pH levels (≤ pH 4.0) were due to lactic and acetic acids and acids derived from fruit juice flavourings. The concentration of lactic acid was significantly greater than acetic acid in each yoghurt (P > 0.05).link_to_subscribed_fulltex