Of the Aeromonas spp. isolated routinely in our laboratory from human feces, about two thirds represent Aeromonas caviae. In contrast to Aeromonas hydrophila and Aeromonas sobria, this species has been considered to be of little enteropathogenic significance due to the absence of known virulence factors. The clinical data presented here suggest a clinical significance of A. caviae, at least in some cases. As yet nothing is known about the pathogenic mechanisms involved.