The use of bleomycin-Fe(II) complex in the determination of DNA crosslinks by alkaline elution was investigated for the purpose of developing a simple nonradiometric method applicable for detection of DNA damage in marine organisms. The assay involves preparation of active bleomycin-Fe(II) complex and its application in the washing step of the original alkaline elution procedure. Treatment of cell-free DNA from Friend leukemia cells and mussel hemolymph with bleomycin-Fe(II) complex directly on the filter resulted in a concentration-dependent strand scission response with excellent correlation (r = 0.94 and 0.98, respectively). The procedure was validated by determination of DNA cross-links in mussels injected with mitomycine C and formaldehyde.