CD44 is a cell surface adhesion molecule postulated to control lymphocyte recirculation by facilitating entry into lymphoid tissue. Tumour cells transfected to overexpress the epithelial variant CD44R1 readily gain access to lymph nodes and distant metastatic sites in animal models, possibly by mimicking circulating lymphocytes. To investigate if human tumours display altered CD44 expression we performed reverse transcriptase a polymerase chain reaction (PCR) analysis of CD44 in 49 specimens from normal colonic mucosa, primary colon and rectal tumours, normal liver, and metastases of 20 patients. The haematopoietic variant CD44H was the principal isoform amplified in all of the specimens, However, 12/14 primary tumours and 16/16 metastatic potential. Moreover, the relative increase with only 2 of 13 normal mucosa specimens. This increase in CD44R1 relative to CD44H expressed by human colon carcinoma cells may increase their metastatic potential. Moreover, the relative increase in PCR amplification of CD44R1 compared with that of CD44H may provide a sensitive method for detecting primary and metastatic colon carcinoma cells in small biopsy specimens.