Biochemical analysis of CF preparations identified three major classes of endogenous chemical clastogens: (i) lipid peroxidation products derived from arachidonic acid of membranes, and in particular the highly clastogenic aldehyde 4-hydroxynonenal (Emerit et al. 1991), (ii) cytokines such as tumor necrosis factor alpha (Emerit et al. 1995a), and (iii) unusual nucleotides such as inosine di-and triphosphate (Auclair et al. 1994). Here, TNF is linked to cystic fibrosis.