Abnormal levels of soluble intercellular adhesion molecule-1 (sICAM-1), C-reactive protein (CRP) and von Willebrand factor (vWf) are commonly found in breast and other cancers. However, the relationship between these molecules is unclear as raised sICAM-1 and vWf may simply reflect an acute phase response. We tested the hypothesis that raised sICAM-1 and vWf are related to the acute phase response by measuring both markers by enzyme-linked immunosorbent assay, and CRP by dry chemistry, in 40 women with breast cancer (cases) and 40 age-matched controls. All three markers were raised in the cases compared with the controls [sICAM-1 (mean +/- SD), 281 +/- 70 versus 230 +/- 40 ng/ml; vWf (mean +/- SD), 139 +/- 33 versus 106 +/- 16 IU/dl; CRP (median), 7 (interquartile range, 5-11) versus 5 (4-6) mg/dl; all P < 0.01]. However, sICAM-1 correlated strongly with CRP (r = 0.67, P < 0.001) in the cases but there was no significant relationship between vWf and CRP (r = -0.15, P = 0.351). There were no significant correlations in the controls. We conclude that raised sICAM-1 in breast cancer, like the acute phase response, reflects inflammation, and that raised vWf seems likely to be independent of the acute phase response.