Twenty-eight fresh and seven type strains of Lactobacillus species were tested for their ability to grow and metabolize glucose in the presence of fluoride. While there was variation between the test organisms, freshly isolated strains were generally more fluoride-tolerant than were the type strains, and a group of seven strains would grow well at pH 4.5 with 5.3 mm NaF. Glucose metabolism by representative strains of this latter group required average fluoride concentrations of 204, 64, and 9.3 mM to inhibit glycolysis completely at pH 7.0, 6.0, and 5.0, respectively. These values are ten times higher than those required to inhibit glucose metabolism by Streptococcus mutans.