Increased concentrations of soluble intercellular adhesion molecule-I (ICAM-1) have been reported in a number of diseases including cancer. This study was undertaken to evaluate soluble ICAM-1 in colorectal cancer and its relationship to an unspecific acute phase response. Fifty six patients (25 with advanced colorectal cancer and 31 out-patients after radical surgical treatment) were included. Soluble ICAM-1 was measured by enzyme immunoassay. Four acute phase proteins (C-reactive protein, acid alpha 1-glycoprotein, haptoglobin and ceruloplasmin) were estimated by immuno-nephelometry. No significant increase of soluble ICAM-1 could be demonstrated in the patients compared to a control group (median 273 ng/ml vs. 270 ng/ml). Furthermore, patients with advanced colorectal cancer did not demonstrate elevated soluble ICAM-1 compared to follow-up out-patients. Patients with present acute phase response as determined by C-reactive protein were shown to have increased soluble ICAM-1 compared to patients without acute phase reaction. Using other acute phase proteins no difference for soluble ICAM-1 has been shown. Our data suggest an association between acute phase response and increased ICAM-1 in patients with colorectal cancer which should be considered when the diagnostic and/or prognostic usefulness of soluble ICAM-1 is to be evaluated.