We reason that the failure to detect this type of DNA This paper reports a gravity-flow filter elution assay fragmentation in some model systems may be more that permits the simultaneous detection of DNA douindicative of the limited detection sensitivity of convenble strand breaks (DSBs, as neutral elutable DNA) and tional agarose gel electrophoresis, which only resolves DNA single strand breaks (SSBs, as alkaline elutable small DNA fragments (180 bp to Γ2 kb), than the lack DNA). This assay is based on a modification of a conof DNA double strand fragmentation or apoptosis. ventional gravity-flow alkaline elution procedure. The More sensitive detection methods are needed to test elution fraction resulting from cell lysis before the apthis hypothesis. To that end, pulse-field gel electrophoplication of the alkaline elution buffer provides an esresis analysis has been used to detect the occurrence timate of DNA DSBs, while the fraction eluted by the of larger molecular weight DNA fragments (ΓΊ30 kb) alkaline buffer (pH 12.3) measures the extent of DNA (6, 7), but the initial investment in instrumentation SSBs. Data show that, in addition to its good detection remains prohibitive for many laboratories. As an altersensitivity for SSBs, this method provides a sensitive native, we report in this paper an inexpensive yet sensimeasure of DNA DSBs. As an illustration of its specitive filter elution assay capable of simultaneous detecficity, this method unambiguously distinguished DNA tion of DNA DSBs and DNA single strand breaks SSBs induced by X-irradiation of mouse leukemia (SSBs). L1210 cells from DNA DSBs occurring in cells undergo-Ionizing radiation (X ray, g-ray) and certain genoing nucleosomal DNA fragmentation and apoptosis. toxic agents induce DNA SSBs (8). Extensive DNA