Growth of human clinical isolates of Streptococcus constellatus, Strep. intermedius and Strep. anginosus in HCl-, acetate and lactate acidified media was investigated. Under aerobic conditions, Strep. constellatus and Strep. anginosus were significantly more tolerant to all the acidulants than was Strep. intermedius. Under anaerobic conditions, Strep. anginosus and Strep. intermedius were significantly more tolerant to acetic acid (pH < 4.5) than Strep. constellatus.