An in vitro method is described which allows radiation dose response data to be obtained for samples of oesophageal mucosa obtained from patients undergoing resection for adeno or squamous cell carcinoma. Data are obtained using a growth endpoint from explant cultures and may be expressed in terms of absolute growth inhibition or reduced rate of growth. Radiation dose response curves suggest that cell survival is in the range expected for mammalian cells but that, as is found clinically, tumour cells are far more resistant to radiation than normal cells. The technique provides a means of assessing differential radiation response in normal and tumour tissues from the same patient, as it is unusual for both to be amenable to clonogenic assay.