Monolayers of HeLa cells were treated with lipopolysaccharide (LPS) or alkali-treated lipopolysaccharide (aLPS) from Salmonella typhimurium 395 MS (wild) and MR10 (chemotype Rd), and the effects on subsequent adhesion of MS and R10 bacteria determined. R10 LPS increased the adhesion of both R10 and MS bacteria; more so for R10. MS aLPS increased the adhesion of R10 bacteria and to some extent of MS. MS LPS and R10 aLPS had only small effects. Significant inhibition of bacterial adhesion could not be found with any of the LPS preparations used. aLPS had greater affinity than LPS for HeLa cells. HeLa cells did not lose viability after treatment with LPS or aLPS. These results indicate that LPS and aLPS may change the properties of the HeLa cell surface and expose areas amenable to interact with bacteria.