Thirteen clinical Aeromonas caviae isolates from the faeces of 13 children with mild to severe diarrhoea were tested for enhancement of mouse lethality, adhesion ability, siderophore and cholera toxin cross-reactive (CTC) factor production, by four consecutive passages through mice by intraperitoneal injection of A. caviae suspensions. The passaged A. caviae strains were re-isolated from monomicrobic cardiac blood samples and inocula were prepared for the next passage. All A. caviae isolates possessed the ability to adhere to the mucosal epithelial surface of the rabbit small intestine. Serial passage in mice showed that the virulence of some isolates for mice was increased in terms of percentage mortality and a lowering of the LD50. For some of the isolates, but not all, serial passage appeared to increase siderophore production and adhesion to rabbit small intestinal cells. For the A. caviae isolates tested, increased values of the CTC factor were observed after passage. A clear correlation was observed between the lowering of LD50 and the enhancement of CTC factor production after passage in mice. These results indicate that the A. caviae isolates possessed virulence factors.