Abstract Survival and extracellular matrix gene expression were studied by viable cell count assay and Northern transfer analysis to compare the sensitivity of normal skin and keloid fibroblasts towards x-irradiation. As the dosage of radiation increased, the numbers of viable cells in irradiated groups were remarkably decreased exponentially, with no significant difference between normal and keloid cell lines. By Northern blot analysis, there was no change in size of the mRNAs for pro α1(I) collagen, fibronectin and β-actin. By slot-blot hybridization, pro α1(I) collagen mRNA levels in x-irradiated fibroblasts were markedly decreased compared with non-irradiated controls. The amounts of fibronectin and β-actin mRNAs were also decreased. This study suggests that both normal skin and keloid fibroblasts are sensitive to x-irradiation, and that extracellular matrix gene expression is also affected by such exposure.