Although radiotherapy can provide effective cancer treatment, tumors and cancer cells exhibit wide variations in sensitivity to radiation killing. To explore the basis of that variation, Amundson and colleagues compared radiation survival with gene expression responses in the NCI-60 cancer cell lines. A small set of radiation-induced genes was associated with low survival, separating the more sensitive cell lines after a 2-Gy dose, as illustrated by multidimensional scaling. Basal gene expression patterns, however, appeared more strongly correlated with survival, and differentiated the sensitive lines more clearly. Basal gene expression levels may ultimately prove more useful than radiation response profiles for predicting the outcome of radiotherapy. For details, see the article by Amundson and colleagues on page 415 of this issue.