[en] Analysis of DNA fragmentation and repair in relation to radiation quality may give important information about the role of break complexity and correlated double strand breaks (DSBs). DNA fragment analysis was performed by pulsed-field gel electrophoresis after exposure to different radiation qualities. Normal human fibroblasts were irradiated with boron ions (40, 80 and 160 keV.μm^-1), nitrogen ions (80, 125, 175 and 225 keV.μm^-1) and neon ions (225 and 300 keV.μm^-1). The amount of DNA less than 1.1 Mbp decreased with increasing linear energy transfer (LET) for all three ions. When theoretical random distributions were subtracted from the experimental data for 225 keV.μm^-1 nitrogen ions in all size intervals (5-5700 kbp), there was a significant non-random distribution of DSBs for sizes up to 1-3 Mbp. This non-random distribution of breaks, probably produced by intra-track correlated DSBs, may constitute a substantial portion of the high-LET induced DSBs. (author)