A panel of 13 human colorectal cell lines was studied, with these lines exhibiting a histological profile similar to that observed in clinical practice. In the five lines tested, variable sensitivity to radiation was observed, from the relatively sensitive NCI-H716 to the highly resistant line NCI-H630, with the latter cell line derived from a patient who had previously received radiation treatment. Glutathione levels and glutathione related enzyme activity varied widely between all 13 cell lines, showing no relationship to radiation sensitivity. The variability observed suggests that some colonic tumours may be responsive to radiation, although their identification remains difficult. However, this may prove possible by incorporation of recently developed cell adhesive matrix assays using survival following a 2 Gy radiation dose as a parameter of radiation sensitivity. This panel of human cancer cell lines offers an ideal model for the study of parameters affecting the radiosensitivity and chemosensitivity pattern of colorectal cancer cells.