During development differentcells of multicellular organisms die by a physiological process referred to as programmed cell death or apoptosis (1). In difference to necrosis the apoptotic death requires de novo protein synthesis (2) and is therefore often called cellular suicide. Besides cell morphology fragmentation of chromatin into units of single or multiple nucleosomes is specific for apoptosis and one of the easiest ways to distinguish programmed cell death and toxic necrosis. Besides more sophisticated techniques like cytofluorometry after staining of cells with propidium iodide (3) andin situ labelling with terminal nucleotidyltransferase (4) the appearance of the nucleosomal DNA ladder in agarose gels has become the hallmark of programmed cell death. The isolation of apoptotic DNA is performed either with isolated nuclei (3, 5) or with total cells (4, 6). In most protocols intact chromatin compromises handling of the samples, especially if the proportion of apoptotic cells is low.

Here we describe a simple and reproducible technique for the isolation ofapoptotic DNA fragments. The method works without time consuming organic extractions and is suitable for the management of a high number of samples. After harvesting the cell samples are washed with phosphate buffered saline and pelleted by centrifugation. The cell pellets are then treated for 10 s with lysis buffer (1% NP-40 in 20 mM EDTA, 50 mM