Numerous studies had linked human cytomegalovirus (HCMV) infections with neoplasia. Among various other malignant tumors, colonic carcinoma tissues were reported to contain DNA sequences hybridizing with DNA extracted from virus particles. Gene technology allowed us to use a cloned viral DNA library to measure HCMV in colorectal tumors more specifically. Four of 38 tissue specimens did contain DNA sequences homologous to cloned viral DNA probes; however, in each of those cases, identical hybridization patterns were seen with specimens from non-infiltrated surrounding intestinal wall. The amount of HCMV DNA in normal tissues was at least as much as in tumor biopsies. We conclude that nucleic acid hybridizations at high sensitivity with moleculary cloned HCMV DNA did not support the notion of a correlation between colorectal carcinomas and human cytomegalovirus.