The ability of Prevotella intermedia to bind type I collagen was investigated. A simple method in which bacterial cells were allowed to attach to collagen-coated microtitre plate wells was used to characterize the activity. All strains of P. intermedia tested, as well as those of the closely related species Prevotella nigrescens, showed a capacity to attach to the collagen film. Exponential-phase cultures of P. intermedia demonstrated a greater binding capacity than older cells. Attachment to the collagen film was inhibited by the presence of EDTA, type I and IV collagen, denatured collagen (gelatin), fibrinogen or fibronectin. Pretreatment of bacterial cells with heat (60 degrees C, 30 min) or proteinase K also inhibited the binding. The collagen-binding activity could be solubilized from the bacterial cell surface by incubation with Zwittergent 3-14, a zwitterionic detergent. The collagen-binding capacity of P. intermedia demonstrated in the present study represents a mechanism of colonization allowing these bacteria to attach to a tissue matrix.