I-125-labeled type I collagen (Cn-I) binding of 92 fresh isolates and 18 type culture collection strains of lactobacilli was tested. More than 75% of the strains bound Cn-I. The binding was inhibited by excess of unlabeled Cn-I, gelatin, and was sensitive to proteinase K. Other proteins such as fibronectin and albumin and various carbohydrates such as D-galactose, D-fucose, and D-mannose did not inhibit the binding. Therefore, we propose binding of Cn-I to lactobacilli involving specific surface protein(s).