Treatment of NSCLC cell lines with As-Rad51 resulted in a significant reduction of Rad51 foci in all cell lines and corresponds to a reduction in dose equivalents from 30 Gy to <2 (A549), ⩽5 (H460, H661) and ⩽10 Gy (H520). The gene discussed is RAD51; the disease is non-small cell lung carcinoma.