An in vitro model was developed to quantitatively measure bacterial adherence to the surface of prosthetic vascular graft material. Four strains of bacteria (Staphylococcus aureus, nonmucin-producing S. epidermidis [SP-2], mucin-producing S. epidermidis [RP-12], and Escherichia coli) were used to inoculate expanded polytetrafluoroethylene (ePTFE), woven Dacron, and velour knitted Dacron graft material. After graft specimens were incubated in a 10(7) suspension of bacteria, they were washed to remove nonadherent organisms and ultrasonically oscillated to dislodge adherent organisms. Quantitative culture of the sonication effluent was used to calculate bacterial adherence, expressed as the number of colony-forming units found in each square centimeter of graft material per 10(7) inoculum. All bacterial strains had a greater affinity to velour knitted Dacron graft than to ePTFE (p less than 0.025). E. coli and S. aureus adhered to velour knitted Dacron in greater numbers than to woven Dacron (p less than 0.04). The production of extracellular polysaccharide (mucin) by the RP-12 strain significantly increased adherence to both EPTFE and Dacron grafts compared with the other three bacterial strains tested (p less than 0.04). Although E. coli was less adherent to ePTFE than nonmucin-producing staphylococcal strains (S. aureus and SP-2), no difference in adherence to knitted or woven Dacron graft material was demonstrated. The differential adherence of bacteria to prosthetic vascular grafts pays an important role in the pathogenesis of graft sepsis and determines relative graft infectivity. The in vitro model developed is well suited for further study of the mechanisms by which bacteria adhere to and colonize vascular grafts.