The high prevalence of serum neutralizing antibodies against Inoue-Melnick virus (IMV) among American patients with colorectal carcinoma has been confirmed. Sera from 26 patients with colorectal carcinoma along with the identical number of age- and sex-matched patients with non-colorectal neoplasia and normal healthy controls were collected in the Buffalo area. All of the colorectal carcinoma group possessed antibodies against IMV (100%), while antibody positivity for non-colorectal neoplasia and for normal controls were 34.6% and 38.5%, respectively. Geometric mean titers of antibodies to IMV type 1 and type 2 for colorectal carcinoma were 266 and 338, respectively, whereas the mean titers in the other two control groups were less than 10.3. These differences between colorectal carcinoma and the two controls were highly significant (P less than 0.001). The majority of patients with colorectal carcinoma had antibodies to both IMV types 1 and 2.